The defender has joined the Italian giants from Argentinian side Lanus and has signed a five-year deal.
An AC Milan club statement read: "AC Milan have met a great professional with a great passion for football and wants to warmly welcome him.
"The Paraguayan, defending champion in Argentina with Lanus, Gustavo Gomez has signed a contract with our club until June 30, 2021".
New arrival at #ACMilan: #WelcomeGomez!
— AC Milan (@acmilan) August 5, 2016
Nuovo arrivo in Casa Milan: benvenuto @gustavogomez462pic.twitter.com/xM9gvD40b3