After ten consecutive seasons with Milan and 306 competitive appearances for the team, Abate became a free agent in July 2019 and announced his retirement as a player in 2020.

[7] Abate started playing football with amateur club Rescaldina, before joining AC Milan's youth system in 1999.

He made his debut, in European competitions, in a Champions League group-stage game versus Celta Vigo on 9 December.

[9] In that match, he set the record as the youngest Milan player to ever play in the UEFA Champions League, at 17 years and 27 days.

[20] After serving mainly as a reserve midfielder in the first few games, he later started to be employed as the regular right back by Milan head coach, Leonardo.

His dribbling skills and speed in the right wing allowed him to outrun opponent defenders, while his crossing into the centre also resulted in goals regularly.

One notable moment for him occurred on 22 February 2016, when he made an excellent sliding tackle on Lorenzo Insigne on the right wing, preventing him from scoring a second goal in a 1–1 away draw against Napoli.

In late March 2017, after initially being sidelined for Milan's following fixtures against Chievo, Juventus, and Genoa, Abate was ruled out for the remainder of the 2016–17 season, due to requiring surgery after suffering "blunt force trauma" to his left eye, after being hit by a ball in the face during a match against Sassuolo on 26 February.

[24] In late 2018, Abate temporarily assumed the role of a centre-back in the wake of an unexpected severe injury crisis that struck the team's defence.

In this role, he was praised for his performances by the club's coach, Gennaro Gattuso, and various Italian media outlets alike.

During the match, the Milan Ultras of the Curva Sud saluted him by holding up a banner with the message "10 years of commitment and humility.

[27] With the Olympic national team coached by Casiraghi, he won the 2008 Toulon Tournament, in which he played four games and scored a goal against the United States.

Nearly two years after his debut, Abate scored his first international goal in a friendly match against Germany in November 2013, which ended in a 1–1 draw.