Abbé Nicolas Louis de Lacaille (March 15, 1713 – March 21, 1762) was a French astronomer.

He is noted for his catalogue of nearly 10,000 southern stars, including 42 nebulous objects. This catalogue, called Coelum Australe Stelliferum, was published posthumously in 1763. It introduced 14 new constellations which have since become standard. He also calculated a table of eclipses for 1800 years. In honor of his contribution to the study of the southern hemisphere sky, a 60-cm telescope at Reunion Island will be named La-Caille telescope

Born at Rumigny, Ardennes, he was left destitute by the death of his father, who held a post in the household of the duchess of Vendôme. Therefore, his theological studies at the College de Lisieux in Paris were undertaken at the expense of the duke of Bourbon. After he had taken deacon's orders, however, he concentrated on science, and, through the patronage of Jacques Cassini, obtained employment, first in surveying the coast from Nantes to Bayonne, then, in 1739, in remeasuring the French arc of the meridian, for which he is honored with a pyramid at Juvisy-sur-Orge. The success of this difficult operation, which occupied two years, and achieved the correction of the anomalous result published by J. Cassini in 1718, was mainly due to Lacaille's industry and skill. He was rewarded by admission to the Academy and the appointment of mathematical professor in Mazarin college, where he worked in a small observatory fitted for his use.

His desire to observe the southern heavens led him to propose, in 1750, an astronomical expedition to the Cape of Good Hope. This was officially sanctioned by Roland-Michel Barrin de La Galissonière. Among its results were determinations of the lunar and of the solar parallax (Mars serving as an intermediary), the first measurement of a South African arc of the meridian, and the observation of 10,000 southern stars. On his return to Paris in 1754 Lacaille was distressed to find himself an object of public attention; he withdrew to Mazarin college, where he worked actively for some years, and there died of an attack of gout aggravated by over-work in 1762.

Lalande said of him that, during a comparatively short life, he had made more observations and calculations than all the astronomers of his time put together. The quality of his work rivalled its quantity, while the disinterestedness and rectitude of his moral character earned him universal respect.

In 1754, de Lacaille was elected a foreign member of the Royal Swedish Academy of Sciences.

The crater La Caille on the Moon is named after him. Asteroid 9135 Lacaille, discovered on 17 October 1960 by Cornelis Johannes van Houten, Ingrid van Houten-Groeneveld and Tom Gehrels at Palomar Observatory, was also named after him.