Thomas Newcomen was a lay preacher and a teaching elder in the local Baptist church. After 1710 he became the pastor of a local group of Baptists. His father had been one of a group who brought the well-known Puritan John Flavel to Dartmouth. Later one of Newcomen's Business contacts in London, Edward Wallin, was another Baptist minister who had connections with the well-known Doctor John Gill of Horsleydown, Southwark. Newcomen's connection with the Baptist church at Bromsgrove materially aided the spread of his steam engine, as the Engineers Jonathan Hornblower (both father and son) were involved in the same church.
Newcomen's great achievement was his steam engine, developed around 1712; combining the ideas of Thomas Savery and Denis Papin, he created a steam engine for the purpose of lifting water out of a tin mine. It is likely that Newcomen was already acquainted with Savery, whose forebears were merchants in south Devon. Savery also had a post with the Commissioners for Sick and Hurt Seamen, which took him to Dartmouth. Savery had devised a "fire engine", a kind of thermic syphon, in which steam was admitted to an empty container and then condensed. The vacuum thus created was used to suck water from the sump at the bottom of the mine. The "fire engine" was not very effective and could not work beyond a limited depth of around thirty feet.
Comparatively little is known of Newcomen's later life. After 1715 the engine affairs were conducted through an unincorporated company, the 'Proprietors of the Invention for Raising Water by Fire'. Its secretary and treasurer was John Meres, clerk to the Society of Apothecaries in London. That society formed a company which had a monopoly on supplying medicines to the Navy providing a close link with Savery, whose will he witnessed. The Committee of the Proprietors also included Edward Wallin, a Baptist of Swedish descent; and pastor of a church at Maze Pond, Southwark. Newcomen died at Wallin's house in 1729, and was buried at Bunhill Fields burial ground on the outskirts of the City of London: the exact site of his grave is unknown.
The Newcomen engine held its place without material change for about 75 years, spreading gradually to more areas of the UK and mainland Europe. At first brass cylinders were used, but these were expensive and limited in size. New iron casting techniques pioneered by the Coalbrookdale Company in the 1720s allowed bigger cylinders to be used, up to about 6 feet (1.8 m) in diameter by the 1760s. Experience led to better construction and minor refinements in layout. Its mechanical details were much improved by John Smeaton, who built many large engines of this type in the early 1770s; his improvements were rapidly adopted. By 1775 about 600 Newcomen engines had been built, although many of these had worn out before then, and been abandoned or replaced.
By 1733 about 125 Newcomen engines, operating under Savery's patent (extended by statute so that it did not expire until 1733), had been installed by Newcomen and others in most of the important mining districts of Britain and on the Continent of Europe: draining coal mines in the Black Country, Warwickshire and near Newcastle upon Tyne; at tin and copper mines in Cornwall; and in lead mines in Flintshire and Derbyshire, amongst other places.
The Newcomen Engine was by no means an efficient machine, although it was probably as complicated as engineering and materials techniques of the early 18th century could support. Much heat was lost when condensing the steam, as this cooled the cylinder. This did not matter unduly at a colliery, where unsaleable small coal (slack) was available, but significantly increased the mining costs where coal was not readily available, as in Cornwall. Newcomen's engine was gradually replaced after 1775 in areas where coal was expensive (especially in Cornwall) by an improved design, invented by James Watt, in which the steam was condensed in a separate condenser. The Watt steam engine, aided by better engineering techniques including Wilkinson's boring machine, was much more fuel efficient, enabling Watt and his partner Matthew Boulton to collect substantial royalties based on the fuel saved.
Despite Watt's improvements, Common Engines (as they were then known) remained in use for a considerable time, and many more Newcomen engines than Watt ones were built even during the period of Watt's patent (up to 1800), as they were cheaper and less complicated. Of over 2,200 engines built in the 18th century, only about 450 were Watt engines. Elements of Watt's design, especially the Separate Condenser, were incorporated in many "pirate" engines. Even after 1800 Newcomen type engines continued to be built and condensers were added routinely to these. They were also commonly retro-fitted to existing Newcomen engines (the so-called "pickle-pot" condenser).
In 1964 the Newcomen Society of London arranged for a Newcomen engine at Hawkesbury Junction, Warwickshire to be transferred to Dartmouth, where it can be seen working using a hydraulic arrangement instead of the steam boiler. According to Dr. Cyril Boucher of the Newcomen Society, this Newcomen Memorial Engine dates from about 1725, with new valve gear and other parts added later.
On 23 February 2012 the Royal Mail released a stamp featuring Newcomen's atmospheric steam engine as part its "Britons of Distinction" series.
Perhaps the last Newcomen-style engine to be used commercially – and the last still remaining on its original site – is at the Elsecar Heritage Centre, near Barnsley in South Yorkshire. It was restored to working condition between 2012 and 2015, the refurbished engine was unveiled by Prince Edward, Earl of Wessex, in May 2016/ Another Newcomen engines that can be shown working is the modern replica engine at the Black Country Museum in Dudley, West Midlands. The Newcomen Memorial Engine at Dartmouth can be seen moving, but is worked by hydraulics.