Gian (Giovanni) Domenico Mansi (16 February 1692 – 27 September 1769) was an Italian prelate, theologian, scholar and historian, known for his massive works on the Church councils.

In 1758, after a sojourn at Rome, where he had been received by Cardinal Passionei, there was question of elevating him to the Sacred College, but his collaboration in an annotated edition of the famous Encyclopédie displeased Clement XIII.

Three years after his elevation to the episcopate he was smitten with an attack of apoplexy which left him suffering, deprived of the power of motion, until his death.

In the opinion of Auguste Boudinhon, the French priest and canonist who profiled Mansi for The Catholic Encyclopedia, he was "an indefatigable worker, widely read and thoroughly trained, his output was chiefly of a mechanical order, and unoriginal because hurried".

The only work worth mentioning that is all Mansi's own is his Tractatus de casibus et censuris reservatis, published in 1724, which brought him into difficulties with the Index Librorum Prohibitorum.