[5] On 8 July, the club announced the signing of Hugo Boumous from Mumbai City FC on a record transfer fee which is believed to be $280,000 in a first time ever in India, a 5-year deal.

[6][7] On the other hand, ATK Mohun Bagan defender Sandesh Jhingan moved to Croatia after agreeing to a free transfer deal with HNK Šibenik.

Meanwhile Antonio Habas returned home in Spain and said the need of a break for the players was essential after the AFC Cup group stage matches involving intense and painstaking work in 7 days.

[15] The club mutually agreed to terminate the contract of their first choice goalkeeper, Arindam Bhattacharya, who also won the Golden Glove in the previous season, and moved to their city rivals, SC East Bengal.

After a numerous speculations, on the next evening, FC Goa president announced that their serving head coach, Juan Ferrando had decided to join ATK Mohun Bagan, through a buy-out clause.

Ferrando joined the camp on 21 December and faced NorthEast United FC the same evening, which ended with his first win as the ATK Mohun Bagan head coach.

[24] The next match, against Odisha FC, was postponed as one of the players of ATK Mohun Bagan, reportedly Krishna, tested COVID-19 positive on the matchday.

Before the second Derby of the season, the club announced the arrival of veteran Indian goalkeeper Subrata Paul on loan from Hyderabad FC.

[39] On the final matchday, with at least a two goals margin win required to become the ISL Premiers, the team lost against Jamshedpur FC and finished 3rd in the league table.

[47][48] In the opening match of AFC Cup Group D, ATK Mohun Bagan suffered a loss of 4–2 against Gokulam Kerala FC.

[49] The team got back and cruised past Bashundhara Kings and Maziya S&RC with dominating performances to qualify for the inter-zone play-off semi-final.