The Lacaille family had their origins in Paris, where Pierre I de la Caille was established as goldsmith around 1540. His son Pierre II followed the same business, with some military interruptions in service for King Henri IV. Pierre II had 13 children including 12 boys, who became advocates at the Parliament, cavalry men in the Royal guard, printers, publishers, and again goldsmiths. One of them, Pierre III, settled to Rumigny (Ardennes). His son, Raulin became provost of the barony of Gonzague, and was appointed as police official by the Duchess of Guise, an aunt of Charles de Gonzague. Raulin had two sons, Pierre (born 1611) and Charles (born 1645). Pierre followed his father in the judical appointment, while Charles was appointed as a clerk of the court at Rumigny. Charles had six daughters and three sons; two of the sons ran clerical careers while the third was Charles-Louis, father of Nicholas Louis.
Charles-Louis first served as an officer in the artillery and then in the royal guard. In peace times he got engaged in commerce and studied applied and engeneering sciences, in particular mechanics, and constructed some machines of his own invention. First living in some prosperrity, he ruined himself by attempting to run a paper mill which failed. The Duke of Bourbon, minister from 1723 to 1726, put him at the head of a colonial project scheduled for America in 1725 and sent him to Nantes for some time, until the project was abandoned. Charles-Louis then was appointed by the Duchess of Vendôme as a guardian and huntsman at Anet, west of Paris, a post formerly hold by Pierre III.
The young Nicholas Louis spent his first years at Rumigny, living in the house of his birth, a considerable building, under tuition of his father. He then studied the humanities at the college of Mantes-sur-Seine, northwest of Paris, until 1729. In the two years following, he went to study rhetoric at the college of Lisieux in Paris, where he actually studied a multitude of topics in history, antiques, mythology, and Latin poetry. When his father died in 1731, he left him with a heavy load of debts and without resources. Nevertheless, Nicholas Louis completed his philosophical studies, because of a good reputation for assiduity and support by his patron, the Duke of Bourbon. Afterwards, he enroled for a three-year study at the college of Navarre, for obtaining ordination for priesthood. During this time he first contacted mathematics, and did his first private studies of astronomy.
In 1736, he finally graduated to a Master of Arts and Bachelor of Theology, but the circumstances around this graduation caused him to turn away from formal theology. Evans (1992) reports, in contrast to other, less acurate sources, that Lacaille was never ordained, despite him being later known as "Abbé Lacaille." He received minor orders as a deacon, and was attached to the chapel of the Collège Mazarin.
He started to work with Jacques Cassini (Cassini II) and Jean-Dominique Maraldi (Maraldi II) at Paris Observatory, and became involved in the geodesic survey of France in 1739 and 1740.
In 1741, he was elected to the Royal Academy of Sciences in Paris. He took his post in the Collège Mazarin, established a small observatory, and started to acquire quality astronomical instruments. He began systematic astronomical observations which he reported periodically to the Academy, focussing on Earth's orbit ("Theory of the Sun"), parallaxes, planetary orbits, comets, and star catalogs. Also at that time, he wrote several textbooks on mathematics, astronomy, mechanics, and optics which got a wide circulation, passed through several editions and got translated to a number of foreign languages, sometimes even to Latin. In consequence, he became correspondent of a number of foreign academies, namely of St. Petersburg, Berlin, Stockholm, Bologna, London, and Göttingen.
During his time at the academy, Lacaille got increasingly interested in exploring the southern skies, which were insufficiently known at that time, with the only more serious survey undertaken by Edmond Halley in 1676-1678. On October 21, 1750, at 7:00 in the evening, Lacaille left Paris, and embarked on the ship Le Glorieux, under a Captain M. Daprès, at Lorient, to enter an expedition to the Cape of Good Hope. They left in the morning of November 21. Lacaille reports that in the evening of that day he was seasick, and remained so for three weeks. In the first days of December they passed Madeira, heading for Rio de Janeiro (Brazil) which was reached on January 26, 1751. They had a stay of almost a month, which Lacaille used for numerous physical, geographic and astronomical measurements. On February 25, 1751, the crew set sail and left heading to South Africa, getting sight of the coast on March 30, 1751 and eventually going ashore on April 20, 1751 at the Cape of Good Hope. Lacaille established an observatory and on August 6, 1751, started to scan the southern skies for one year.
During the time until the beginning of August 1752, he determined the positions of 9,800 stars between the celestial south pole and the tropic of Capricorn; among these stars were the 42 "nebulous stars" he described in his catalog. Moreover, he obtained acurate positions for 240 priciple stars, and extracted 1,930 stars visible to the naked eye for creating a planisphere. He delineated 15 new constellations, 14 of which are still in use today, rejecting Halley's former constellation of "Robur Carolinum," and decomposed old constellation Argo into its parts, Carina, Puppis and Vela. He also took numerous measurements of the positions of the Sun, the Moon, Venus and Mars in order to obtain parallaxes.
In August 1752, Lacaille started to undertake geographic measurements and expeditions to explore the country around the Cape. He finally left on March 8, 1753 aboard the Le Prusieux for exploring two islands in the Indian Ocean, the "Ile de France" (Mauritius) and the "Ile de Bourbon" (Réunion). He arrived at Mauritius in April, where he did surveying, carthographic and geographic work as well as astronomical observations for nine months. He finally left on January 16, 1754 to reach Saint Denis on Réunion on January 17, staying on that island for about 6 weeks. On February 26, 1754, Lacaille embarked on the Achille and on the 27th, left Réunion, passing the Cape of Good Hope, and on April 10, the island of St. Helena. On April 15, they reached Ascension island in the southern Atlantic where they took a 4-day stay. Lacaille eventually returned to France on board of the Achille, reaching Lorient on June 4, 1754, and arriving back in Paris on June 28.
Lacaille was honored by naming Moon crater La Caille (23.8S, 1.1 E, 67 km diameter) in 1961. Asteroid (9135) Lacaille was discovered on October 17, 1960 by C.J. van Houten, I. van Houten-Groeneveld, and T. Gehrels at Palomar Observatory, and provisionally designated 7609 P-L; it was later designated 1994 EK6 on an independent observation.