Biography of James Watt, Inventor of the Modern Steam Engine

James Watt, 1736 - 1819. Engineer, inventor of the steam engine
James Watt, 1736 - 1819. Engineer, inventor of the steam engine, by John Partridge; after Sir William Beechey, 1806. Oil on canvas.

 National Galleries Of Scotland / Getty Images

James Watt (January 30, 1736—August 25, 1819) was a Scottish inventor, mechanical engineer, and chemist whose steam engine patented in 1769 greatly increased the efficiency and range of use of the early atmospheric steam engine introduced by Thomas Newcomen in 1712. While Watt did not invent the steam engine, his improvements on Newcomen’s earlier design are widely regarded as having made the modern steam engine the driving force behind the Industrial Revolution.

Fast Facts: James Watt

  • Known For: Invention of the improved steam engine
  • Born: January 19, 1736 in Greenock, Renfrewshire, Scotland, United Kingdom
  • Parents: Thomas Watt, Agnes Muirhead
  • Died: August 25, 1819 in Handsworth, Birmingham, England, United Kingdom
  • Education: Home educated
  • Patents: GB176900913A “A New Invented Method of Lessening the Consumption of Steam and Fuel in Fire Engines”
  • Spouses: Margaret (Peggy) Miller, Ann MacGregor
  • Children: James Jr., Margaret, Gregory, Janet
  • Notable Quote: “I can think of nothing else than this machine.”

Early Life and Training

James Watt was born on January 19, 1736, in Greenock, Scotland, as eldest of the five surviving children of James Watt and Agnes Muirhead. Greenock was a fishing village that became a busy town with a fleet of steamships during Watt's lifetime. James Jr.'s grandfather, Thomas Watt, was a well-known mathematician and local schoolmaster. James Sr. was a prominent citizen of Greenock and a successful carpenter and shipwright who outfitted ships and repaired their compasses and other navigational devices. He also served periodically as Greenock’s chief magistrate and treasurer.

'Watt's First Experiment', 18th century, (c1870). Artist: Herbert Bourne
'Watt's First Experiment', 18th century, (c1870). James Watt (1736-1819) Scottish engineer, as a boy experimenting with the tea-kettle at the dining table of his childhood home at Greenock. In the left background is his father's assistant with a client in the carpenter's shop. Print Collector / Getty Images

Despite showing an aptitude for mathematics, young James' poor health prevented him from attending Greenock Grammar School regularly. Instead, he gained the skills he would later need in mechanical engineering and the use of tools by helping his father on carpentry projects. The young Watt was an avid reader and found something to interest him in every book that came into his hands. By age 6, he was solving geometrical problems and using his mother's tea kettle to investigate steam. In his early teens, he began to exhibit his abilities, particularly in mathematics. In his spare time, he sketched with his pencil, carved, and worked at the tool bench with wood and metal. He made many ingenious mechanical works and models and enjoyed helping his father repair navigational instruments.

After his mother died in 1754, the 18-year-old Watt traveled to London, where he received training as an instrument maker. Though health problems prevented him from completing a proper apprenticeship, by 1756 he felt he had learned enough “to work as well as most journeymen.” In 1757, Watt returned to Scotland. Settling in the major commercial city of Glasgow, he opened a shop on the University of Glasgow campus, where he made and repaired mathematical instruments such as sextants, compasses, barometers, and laboratory scales. While at the university, he became friends with several scholars who would prove influential and supportive of his future career, including famed economist Adam Smith and British physicist Joseph Black, whose experiments would prove vital to Watt’s future steam engine designs. 

James Scott portrait of a young James Watt working on the design of his steam engine, c1769
James Watt as a young man, c1769. Artist: James Scott. Print Collector / Getty Images

In 1759, Watt formed a partnership with Scottish architect and businessman John Craig to manufacture and sell musical instruments and toys. The partnership lasted until 1765, at times employing up to 16 workers.

In 1764, Watt married his cousin, Margaret Millar, known as Peggy, whom he had known since they were children. They had five children, only two of which lived to adulthood: Margaret, born in 1767, and James III, born in 1769, who as an adult would become his father's main supporter and business partner. Peggy died during childbirth in 1772, and in 1777, Watt married Ann MacGregor, daughter of a Glasgow dye-maker. The couple had two children: Gregory, born in 1777, and Janet, born in 1779.

The Path to a Better Steam Engine

In 1759, a student at the University of Glasgow showed Watt a model of a Newcomen steam engine and suggested it might be used—instead of horses—to propel carriages. Patented in 1703 by English inventor Thomas Newcomen, the engine worked by drawing steam into a cylinder, thereby creating a partial vacuum which allowed the increased atmospheric pressure to push a piston into the cylinder. During the 18th century, Newcomen engines were used throughout Britain and Europe, mostly to pump water out of mines.

Drawing of the Newcomen steam engine
Newcomen atmospheric steam engine. Newton Henry Black / Wikimedia Commons / Public Domain

Fascinated by the Newcomen engine, Watt began building miniature models using tin steam cylinders and pistons attached to driving wheels by a system of gears. Over the winter of 1763–1764, John Anderson at Glasgow asked Watt to repair a model of a Newcomen engine. He was able to get it running, but perplexed by its waste of steam, Watt began studying the history of the steam engine and conducted experiments in the properties of steam.

Watt independently proved the existence of latent heat (the heat required to convert water into steam), which had been theorized by his mentor and supporter Joseph Black. Watt went to Black with his research, who gladly shared his knowledge. Watt came away from the collaboration with the idea that set him on the path to an improved steam engine based on his best-known invention—the separate condenser

The Watt Steam Engine

Watt came to realize that the greatest fault in the Newcomen steam engine was poor fuel economy due to its rapid loss of latent heat. While Newcomen engines offered improvements over earlier steam engines, they were inefficient in terms of quantity of coal burned to make steam vs. power produced by that steam. In the Newcomen engine, alternating jets of steam and cold water were injected into the same cylinder, meaning that with each up-and-down stroke of the piston, the cylinder’s walls were alternately heated, then cooled. Each time steam entered the cylinder, it continued to condense until the cylinder was cooled back down to its working temperature by the jet of cold water. As a result, part of the potential power from the steam’s heat was lost with each cycle of the piston.

Illustration showing James Watt's (1736-1819) revolutionary invention with explanatory diagram of its functioning.
James Watts steam Engine at work. Print Collector / Contributor / Getty Images

Developed in May 1765, Watt’s solution was to equip his engine with a separate chamber he called a “condenser” in which condensation of the steam occurs. Because the condensing chamber is separate from the working cylinder containing the piston, condensation takes place with very little loss of heat from the cylinder. The condenser chamber remains cold and below atmospheric pressure at all times, while the cylinder remains hot at all times.

In a Watt steam engine, steam is drawn into the power cylinder under the piston from the boiler. As the piston reaches the top of the cylinder, an inlet valve allowing steam to enter the cylinder closes at the same time a valve allowing steam to escape into the condenser opens. The lower atmospheric pressure in the condenser draws in the steam, where it is cooled and condensed from water vapor to liquid water. This condensation process maintains a constant partial vacuum in the condenser, which is passed to the cylinder by a connecting tube. External high atmospheric pressure then pushes the piston back down the cylinder to complete the power stroke.

Separating the cylinder and condenser eliminated the loss of heat that plagued the Newcomen engine, allowing Watt’s steam engine to produce the same “horsepower” while burning 60% less coal. The savings made it possible for Watt engines to be used not just at mines but wherever power was needed.

However, Watt’s future success was in no way assured nor would it come without hardship. By the time he came up with his breakthrough idea for the separate condenser in 1765, the expenses of his research had left him near poverty. After borrowing considerable sums from friends, he finally had to seek employment in order to provide for his family. During a span of about two years, he supported himself as a civil engineer, surveying and managing the building of several canals in Scotland and exploring coal fields in the neighborhood of Glasgow for the magistrates of the city, all while continuing to work on his invention. At one point, a despondent Watt wrote to his old friend and mentor Joseph Black, “Of all things in life, there is nothing more foolish than inventing, and probably the majority of inventors have been led to the same opinion by their own experiences.”

In 1768, after producing small-scale working models, Watt entered into a partnership with British inventor and merchant John Roebuck to build and market full-sized steam engines. In 1769, Watt was granted a patent for his separate condenser. Watt’s famous patent titled “A New Invented Method of Lessening the Consumption of Steam and Fuel in Fire Engines” is to this day considered one of the most significant patents ever granted in the United Kingdom.

Birmingham James Watt statue
Bronze statue of Boulton, Watt and Murdoch, 'the Golden Boys', gilded in gold, to commemorate their development of the steam engine, Broad Street, central Birmingham, West Midlands, England. Artist Ethel Davies. Heritage Images / Getty Images

Partnership With Matthew Boulton

While traveling to London to apply for his patent in 1768, Watt met Matthew Boulton, owner of a Birmingham manufacturing company known as the Soho Manufactory, which made small metal goods. Bolton and his company were very well known and respected in the mid-18th century English enlightenment movement.

Boulton was a good scholar, with considerable knowledge of languages and science—particularly mathematics—despite having left school as a boy to go to work in his father's shop. In the shop, he soon introduced a number of valuable improvements and he was always on the lookout for other ideas that might be introduced into his business.

He was also a member of the famous Lunar Society of Birmingham, a group of men who met to discuss natural philosophy, engineering, and industrial development together: other members included the discoverer of oxygen Joseph Priestley, Erasmus Darwin (grandfather of Charles Darwin), and the experimental potter Josiah Wedgwood. Watt joined the group after he became Boulton's partner.

A flamboyant and energetic scholar, Boulton made the acquaintance of Benjamin Franklin in 1758. By 1766, these distinguished men were corresponding, discussing among other things the applicability of steam power to various useful purposes. They designed a new steam engine and Boulton built a model, which was sent to Franklin and exhibited by him in London. They had yet to become aware of Watt or his steam engine.

When Boulton met Watt in 1768, he liked his engine and decided to buy an interest in the patent. With Roebuck's consent, Watt offered Boulton a one-third interest. Although there were several complications, eventually Roebuck proposed to transfer to Matthew Boulton one-half of his proprietorship in Watt's inventions for the sum of 1,000 pounds. This proposal was accepted in November 1769.

Boulton and Watt Working Steam Engines

Sketch showing a steam engine designed by Boulton & Watt, England, 1784.
Boulton & Watt steam engine, 1784. Robert Henry Thurston / Wikimedia Commons / Public Domain

In November 1774, Watt finally announced to his old partner Roebuck that his steam engine had successfully completed field trials. In writing to Roebuck, Watt did not write with his usual enthusiasm and extravagance; instead, he simply wrote: "The fire engine I have invented is now going, and answers much better than any other that has yet been made, and I expect that the invention will be very beneficial to me."

From that point forward, the firm of Boulton and Watt was able to produce a range of working engines with real-world applications. New innovations and patents were taken out for machines that could be used for grinding, weaving, and milling. Steam engines were put into use for transportation on both land and water. Nearly every successful and important invention that marked the history of steam power for many years originated in the workshops of Boulton and Watt.

Retirement and Death

Watt's work with Boulton transformed him into a figure of international acclaim. His 25-year-long patent brought him wealth, and he and Boulton became leaders in the technological Enlightenment in England, with a solid reputation for innovative engineering.

Where Watt Worked
The workshop of Scottish steam engineer and inventor James Watt (1736 - 1819) in Heathfield, where he lived from 1790 until his death. Hulton Archive / Getty Images

Watt built an elegant mansion known as "Heathfield Hall" in Handsworth, Staffordshire. He retired in 1800 and spent the rest of his life in leisure and traveling to visit friends and family.

James Watt died on August 25, 1819 at Heathfield Hall at the age of 83. He was buried on September 2, 1819. in the graveyard of St. Mary's Church in Handsworth. His grave is now located inside the expanded church. 


1787 drawing of a potable James Watt steam engine
1878: A portable James Watt steam engine. Hulton Archive / Getty Images

In a very meaningful way, Watt's inventions powered the Industrial Revolution and innovations of the modern age, ranging from automobiles, trains, and steamboats, to factories, not to mention the social issues that evolved as a result. Today, Watt's name is attached to streets, museums, and schools. His story has inspired books, movies, and works of art, including statues in Piccadilly Gardens and St. Paul's Cathedral.

On the statue at St. Paul's are engraved the words: "James Watt … enlarged the resources of his country, increased the power of man, and rose to an eminent place among the most illustrious followers of science and the real benefactors of the world."

Sources and Further Reference

  • Jones, Peter M. "Living the Enlightenment and the French Revolution: James Watt, Matthew Boulton, and Their Sons." The Historical Journal 42.1 (1999): 157–82. Print.
  • Hills, Richard L. "Power from Steam: A History of the Stationary Steam Engine." Cambridge: Cambridge University Press, 1993.
  • Miller, David Philip. "'Puffing Jamie': The Commercial and Ideological Importance of Being a ‘Philosopher’ in the Case of the Reputation of James Watt (1736–1819)." History of Science, 2000,
  • "The Life and Legend of James Watt: Collaboration, Natural Philosophy, and the Improvement of the Steam Engine." Pittsburgh: University of Pittsburgh Press, 2019.
  • Pugh, Jennifer S., and John Hudson. "The Chemical Work of James Watt, F.R.S." Notes and Records of the Royal Society of London, 1985.
  • Russell, Ben. "James Watt: Making the World Anew." London: Science Museum, 2014.
  • Wright, Michael. "James Watt: Musical Instrument Maker." The Galpin Society Journal 55, 2002.

Updated by Robert Longley

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Bellis, Mary. "Biography of James Watt, Inventor of the Modern Steam Engine." ThoughtCo, Aug. 29, 2020, Bellis, Mary. (2020, August 29). Biography of James Watt, Inventor of the Modern Steam Engine. Retrieved from Bellis, Mary. "Biography of James Watt, Inventor of the Modern Steam Engine." ThoughtCo. (accessed May 30, 2023).