He was born to a recently ennobled family of Venice, received a Jesuit education in Bologna and became a Cardinal-Deacon of San Nicola in Carcere in 1737. Previously he had filled various important posts in the Curia and had been bishop of Padua since 1743; during his tenure as bishop of Padua he visited all the parishes in the diocese, the first bishop to do that for 50 years. He became pope on 6 July, 1758. In the same year the Rezzonico family were celebrating Ludovico Rezzonico's marriage into the powerful Savorgnan family. The son of the man who bought the unfinished palace on the Grand Canal (now Ca' Rezzonico) and finished its construction, Carlo the pontiff was notorious for his rampant nepotism.