Carlo Gonzaga (died 21 December 1456), Lord of Sabbioneta, was an Italian nobleman of the Mantuan House of Gonzaga who rose to the position of Captain of the People in the Ambrosian Republic of Milan, and eventually ruled practically as an autocrat. He was the younger son of Gianfrancesco Gonzaga and Paola Malatesta, as well as a friend of the humanist writer Francesco Filelfo. His brother was the famous Ludovico III Gonzaga, Marquis of Mantua, and became a rival of his for Mantua and in the field of battle.
Carlo Gonzaga was born in Mantua. He married twice, first to Lucia d'Este, daughter of Niccolò III d'Este, who died childless, and then to Ringarda Manfredi, who gave him three daughters and a son.
After the death of his father in 1444 Ludovico became Marquis and removed all authority from Carlo. He went to Venice and fought in her service against the Ambrosian Republic until he defected with Francesco Sforza in 1447. He was appointed Captain of the People in November of that year. He eventually counseled Giovanni Appiano and Giovanni Ossona, the leaders of the Guelphs, in their term in leadership, becoming so powerful that he was raised in all but name to the status of a dictator. He had a lavish house and started replacing men in government to those in his favor. A Ghibelline conspiracy rose against him and his government, but he shattered it, and his Guelph underlings massacred many Ghibellines.
Gonzaga made attempts for peace first with Republic of Venice, then with Francesco Sforza, offering the latter the city of Crema. Gonzaga was thrown into jail at first, but shortly after pardoned with many other Guelphs, and made head of a temporary government until the coronation of Sforza. Later, furious at Sforza for making an alliance with Ludovico, he plotted with Guglielmo of Montferrat in 1450 and was thrown into the Pavian prison. He was released when he conceded to give up his war spoils, Alessandria and Tortona.