Giancarlo Guerrini was an Italian water polo player who played defense. He won the 1956 Italian title with S.S. Lasio, then joined Pro Recco with whom he won three Italian championships in a row (1965-67).
With the national team Guerrini won silver at the 1959 Mediterranean Games and the following year he helped Italy win Olympic gold in Roma. Remaining in the national squad even after the end of that sporting cycle, he won the Mediterranean Games again in 1963. In 1964 he was still part of the Italian squad at the Tokyo Olympics where Italy finished fourth. He closed his high-level career with a silver medal at the 1967 Mediterranean Games and played at the 1968 Mexico City Olympics, where Italy placed fourth again. In 2002 he was appointed Knight of Merit of the Italian Republic. He received in 2015 the Gold Collar for Sporting Merit from the Italian National Olympic Committee (CONI).