The 27-year-old, who is currently in Doha with the national team for the upcoming World Cup qualifying matches, was with the then ATK on loan in 2015-16 season, featuring in 13 matches.
"Even though I played in Kolkata before, it was for a very short time. This joining, of course, is going to be a new chapter in my football career," Amrinder, who has turned out for India in six matches, said.
"Winning all the trophies for Mumbai last year was a memorable event in my life. I want the same success in the Green-Maroon jersey next season." Earlier in the day, Mumbai City FC confirmed the departure of Amrinder after an association of five seasons.
In January 4, 2020, Amrinder became the most capped Mumbai City FC player when he led them against ATKMB, bettering the earlier record of Lucian Goian.
Amrinder made 84 appearances for Mumbai City FC with the last match being the 2020-21 ISL final against ATKMB.
Explaining why he joined ATK Mohun Bagan, Amrinder said, "I played for a while in ISL-2 under the coaching of Habas. Everyone knows about his success in ISL.
"Habas' football philosophy always draws me. The biggest thing is that he brought out the best game from the Indian footballers. It's great to be a member of this team.
"The support of a huge number of ATK MB supporters, the football philosophy of the principal owner of the team and the glorious history of football of this city (Kolkata) are the reasons."