Maldini began his playing career with local side Triestina, in 1952, and made his Serie A debut in his first season with the club, on 24 May 1953, in a 0–0 away draw against Palermo. After two seasons with Triestina, Maldini transferred to AC Milan in 1954, where he went on to achieve notable successes both domestically and internationally in the team's starting line-up, also becoming an important figure at the club. He made his debut with the club on 19 September 1954, in a 4–0 league win over his former side, featuring in a Milan team which included several important players at the time, such as Lorenzo Buffon, Francesco Zagatti, Nils Liedholm, Gunnar Nordahl, and Juan Alberto Schiaffino; he immediately broke into the first team and won his first league title in his debut season with the squad. In total, he made 347 appearances for Milan in Serie A, scoring 3 goals, and made 412 appearances for the club in all competitions. Maldini won four league titles with Milan, and also later became the team's captain in 1961, a role which he held for several years, until he left the club, and was succeeded by Gianni Rivera. During his time with Milan, he also won a Coppa Latina, and went on to capture the club's first ever European Cup as team captain in 1963, as Milan defeated Benfica 2–1 at Wembley Stadium on 22 May, with two goals from José Altafini; as a result, Milan became the first Italian side ever to win the trophy, while Maldini became the first Italian captain to lift the cup. He made his final appearance for Milan on 22 May 1966, in a 6–1 home win over Catania, in Serie A. In 1966 he moved to Torino for a season, before retiring in 1967; he made his final Serie A appearance on 28 May, in a 2–1 away defeat to Napoli.