In the course of a long and distinguished career, Contarini traversed the cursus honorum of the Venetian Republic, serving as provveditore, savio, rector, and member of the Senate of Venice.
In the years immediately prior to his election as Doge, he had almost entirely withdrawn from public life, and he appears to not even have considered becoming a Procurator of San Marco.
Following the death of Doge Francesco Molin on 27 February 1655, electors met to elect his successor in March 1655, but were divided and could not agree on a candidate.
They eventually settled on Carlo Contarini as a compromise candidate because he was allied with all factions, and old enough that he was not expected to have a long reign.
Perhaps because of the heavy workload of being Doge, Contarini fell ill in early 1656, and, after a series of failed medical treatments, died in Venice on 1 May 1656.