1846 December 19th. Born in Exeter, New Hampshire to Nathaniel and Abigail Swasey.
He was apprenticed as a machinist at the Exeter Machine Works and was afterwards employed at Pratt and Whitney and became a foreman in the gear-cutting section. He developed a new technique for making gear-tooth cutters.
In 1880 he and Warner formed the Warner and Swasey Co which quickly moved to Cleveland, Ohio. Swasey would perform the engineering and machine development at this company.
The close friends Warner and Swasey built their homes next to each other on Euclid Avenue in Cleveland, a street that was known as "Millionaire's Row".
In addition to army ordnance contracts, the firm of Warner & Swasey became notable for their work on astronomical observatories and equipment. The founders were interested in astronomy as an avocation, and in the field's quest for better optical telescopes, which was burgeoning at the time. They also realized that obtaining contracts to build large astronomical observatories would provide publicity for their company.
In 1885 Swasey completed work at McCormick Observatory on the 45-foot dome, which was the largest in the world, and had a unique, 3 shutter design.
In 1887 Swasey built the mount for the 36-inch refracting telescope at Lick Observatory.
In 1898 he manufactured a dividing engine for the U.S. Naval Observatory that was used to make the meridian circles. Both the building and dome of the Dominion Astrophysical Observatory were made by Warner and Swasey Co.
Other observatory telescopes and components were built by the company at the Kenwood Observatory, Yerkes Observatory, Argentine National Observatory, the Swasey Observatory at Denison University, and the Case Institute Observatory.
From 1904 until 1905 he was the president of the American Society of Mechanical Engineers.
Both Warner and Swasey were amateur astronomers. In 1920 they made a joint donation to the Case Western Reserve University to fund the construction of an observatory. This was named the Warner and Swasey Observatory in their honor, and the observatory was used for research by the Case astronomy department. The observatory maintained by the department today is still known by this name today.
Other donations made by Swasey include the Swasey Chapel at Denison University in Granville, Ohio (1924), a bandstand in Exeter by architect Henry Bacon (1916), a library building to Colgate Rochester Divinity School and the endowment of a chair for a professor of physics at the Case School of Applied Sciences. The chimes in the chapel were included as a memorial to his wife, Lavinia Marston Swasey.
1937 June 15th. Died on the old homestead on the farm where he was born
1937 Obituary 
AMBROSE SWASEY was the founder, with Mr. Worcester R. Warner, of the Warner and Swasey Company, of Cleveland, Ohio. He was a past-president and honorary member of the American Society of Mechanical Engineers, by whom he was awarded the Hoover Gold Medal in 1936, for his distinguished public services. Mr. Swasey commenced his training in the machine tool industry in 1864 at the Exeter Machine Works, Exeter, New Hampshire. In 1869 he met his future partner, Mr. Warner, and shortly afterwards both engineers went to Hartford, Connecticut, where Mr. Swasey was placed in charge of the gearing department of the Pratt and Whitney Company. The Warner and Swasey Company was established in 1880, and specialized in the manufacture of machine tools and the structural parts of astronomical telescopes. The firm introduced several new methods for securing precision and accuracy in their products, which included the structural parts for many of the largest telescopes in the world. Mr. Swasey established in 1914 the Engineering Foundation for furthering research in engineering science, and during the remainder of his life, his contributions to its funds exceeded $100,000.
In 1921 he was elected an Honorary Life Member of the Institution, of which he had been a Member since 1898. His death occurred at his summer home in Exeter, New Hampshire, on 15th June 1937, at the age of 90.