In 1833, Antoine LeCoultre (1803–1881) founded a small workshop in Le Sentier, Switzerland, for the manufacture of high-quality timepieces. In 1844, he measured the micrometre (µm) for the first time and created the world's most precise measuring instrument, the millionometer, capable of measuring to thousandths of a millimetre. In 1847, LeCoultre developed a system that eliminated the need for keys to rewind and set watches, using a push-piece that activated a lever to change from one function to another. In 1851, he was awarded a gold medal for his work on timepiece precision and mechanization at the first Universal Exhibition in London.
Antoine's son, Elie LeCoultre, desired to control all stages of timepiece production, so in 1866 he transformed his workshop into a manufacture, allowing his employees to pool their expertise under one roof. In 1870, LeCoultre began using mechanized processes to manufacture complicated timepiece movements. Within 30 years, LeCoultre had created more than 350 different timepiece calibers, of which 128 were equipped with chronograph functions and 99 with repeater mechanisms. From 1902 and for the next 30 years, LeCoultre produced most of the movement blanks for Patek Philippe of Geneva.
In 1903, Parisian Edmond Jaeger challenged Jacques-David LeCoultre, grandson of Antoine, to manufacture ultra-thin calibers of his design. Out of their relationship emerged a collection of ultra-thin pocket watches, followed by others that eventually, in 1937, officially culminated in the Jaeger-LeCoultre brand. In 1907, French jeweler Cartier, a client of Jaeger's, signed a contract with the Parisian watchmaker under which all Jaeger's movement designs for a period of 15 years would be exclusive to Cartier. The movements were produced by LeCoultre. Also in 1907, the LeCoultre Caliber 145 set the record for the thinnest movement at 1.38 mm. JLC began manufacturing the Atmos clock in 1936 after purchasing the patent from Jean-Leon Reutter, who invented it in 1928. The company was officially renamed Jaeger-LeCoultre in 1937. In 1941, Jaeger-LeCoultre earned the highest distinction from the Neuchâtel Observatory for its tourbillon Caliber 170. In 1982, the Jaeger-LeCoultre museum was established in Le Sentier. In 2009, JLC produced the world's most complicated wristwatch, the Hybris Mechanica à Grande Sonnerie with 26 complications.