Giovanni Cornaro (30 June 1720 – 29 March 1789) was an Italian cardinal.
He was protonotary apostolic from 1742, a member of the Apostolic Signatura from 1743, vice-legate in Bologna (1744-1747) and member of the Roman Rota for the Republic of Venice (from 21 March 1759).
In 1765 he became subdeacon, and was subsequently governor of Rome and vice-Camerlengo of the Holy Roman Church (1775–1778).
His other positions included that of lay abbot of Santa Maria in Sylvis, in Friuli.
He was created cardinal on 1 June 1778, with the titulum of San Cesareo in Palatio.