The Frenchman left Old Trafford at the end of June, having not been offered a new deal, meaning that he had been available on a free transfer this summer.
A number of clubs have been credited with an interest in the experienced attacker, but it has now been confirmed that Greek outfit AEK Athens have secured his signature.
The Yellow and Blacks announced Martial's arrival on social media, while Man United also released a statement wishing the 28-year-old luck in the next stage of his career.
AEK Athens sign Martial on a free transfer
"Anthony Martial has signed for Greek club AEK Athens, following his departure from Manchester United earlier this year," read a statement on Man United's website.
"Matias Almeyda's side were champions in 2023 and finished second last season, behind PAOK, who United will face in the Europa League in November.
"There will, however, be no European football for Martial this term as AEK were eliminated from the Conference League at the play-off stage, by Armenian outsiders FC Noah. We'd like to wish Anthony the best of luck in his new venture, in Greece."
When announcing his departure from Old Trafford, Martial wrote on social media: "Manchester United will always be in my heart.
"This club has left its mark on my career and offered me an incredible opportunity to play in front of you. I'm leaving to take on new challenges, I'll always be a Red Devil and I'll continue to follow the club's results with passion."
Martial spent nine years at Man United, scoring 90 goals
Martial arrived at Man United from Monaco in 2015, and he represented the 20-time English champions on 317 occasions, scoring 90 goals and registering 47 assists in the process.
The forward's best goalscoring season came in 2019-20, when he found the back of the net on 23 occasions in all competitions, but he was restricted to just 19 appearances last term due to injury, and a disappointing campaign saw him manage just two goals.
AEK are 13-time Greek champions, with their last success coming in 2022-23, while they have made a strong start to this campaign, sitting at the top of the division on 10 points.
Martial could be in the squad against Athens Kallithea on Sunday, although the Frenchman is likely to need a period of time to build his fitness, having not made a competitive appearance since last December.