The City Football Group (CFG)-owned side will now make its continental debut in the AFC Champions League 2022 Group Stage.
Sergio Lobera's men started the season strongly and looked the clear front-runners as the season progressed. However, the Islanders struggled in a few games towards the fag end of the season that made their chances of lifting the trophy look bleak.
A final push at the very end of the league, including a final day victory over ATK Mohun Bagan FC, clinched the league title for the Islanders.
Mumbai City FC then had to depend on a penalty shoot-out against FC Goa to enter the final. A Bipin Singh winner made it 2-1 for Mumbai City FC against ATK Mohun Bagan FC, handing them their first-ever ISL title.
With Mumbai City FC joining the winners' circle, let us have a look at the teams with the most number of ISL titles.
#1 ATKFC (3 ISL titles)
The erstwhile ATKFC had won the ISL Cup title three times since the inaugural season of the league in 2014.
The Red and Whites, earlier known as Atletico de Kolkata, finished third in the league table at the conclusion of the regular season in 2014. After two goalless draws in the double-legged semi-final tie with FC Goa, Antonio Lopez Habas' side made the final after winning 4-2 in the shootout.
The Kolkata-based franchise was then pitted against Kerala Blasters FC in the summit clash, where a 95th-minute header from Mohammad Rafique sealed the deal for ATK.
Atletico de Kolkata repeated their title-winning feat in the 2016 season under new manager Jose Francisco Molina. The team sneaked into the top-four and finished fourth in the league stage. ATK then pipped Mumbai City FC 3-2 on aggregate in the semi-finals to set up a final clash with Kerala Blasters FC yet again.
The Kolkata-based franchise prevailed once more over their southern rivals, this time in the penalty shoot-out.
After a couple of disappointing seasons, the management turned to Antonio Lopez Habas yet again in the 2019-20 season. With Habas at the helm, the Red and Whites finished second in the regular league stage. The Kolkata-based side got through to the final after a 3-2 aggregate win over Bengaluru FC.
ATKFC faced Chennaiyin FC in the final, whom they eased past 3-1 to win their third title before the eventual merger with Mohun Bagan FC.
#2 Chennaiyin FC (2 ISL titles)
Chennaiyin FC are the second-most successful side in ISL history. The Marina Machans have won the title in the 2015 and 2017-18 seasons. Marco Materazzi's men finished third in the regular season in 2015 and were pitted against the-then defending champions, Atletico de Kolkata, in the semi-finals.
The Marina Machans eased past the Reds and Whites with a 4-2 aggregate win over the two legs. They faced FC Goa in Goa in the final and showed some stunning resilience to bounce back from a 1-2 deficit to eventually win it 3-2.
Chennaiyin FC won their second title under John Gregory in the 2017-18 season. The southern team finished second in the league standings and faced FC Goa in the semi-finals. The Marina Machans blew away the Gaurs with a dominating 4-1 win over the two legs. The final was an all-south affair in Bengaluru, where John Gregory's men won 3-2 over Bengaluru FC to lift their second ISL title.
#3 Bengaluru FC & Mumbai City FC (1 ISL title each)
Bengaluru FC finished top of the league table in the 2018-19 ISL season. The Blues made the final with a 4-2 aggregate win over NorthEast United FC in the semis. A Rahul Bheke winner in the final against FC Goa clinched the first and only ISL title for Bengaluru FC.
Mumbai City FC are the latest entrants to the winners' club with their scintillating showing in the recently-concluded ISL 2020-21 season.