Papa Diawara scored a late goal in the second half to secure the title for his team with four games to spare.
Kibu Vicuna made three changes to the side that drew 1-1 against Chennai City in the previous game. Komron Tursunov returned after serving a one-match suspension, Dhanachandra Singh was reinstated in the left-back position in place of Gurjinder Kumar and Daniel Cyrus replaced a suspended Cyrus Morante.
His opposite number Stanly Rozario made only one alteration as M Malsawmzuala replaced Justice Morgan.
It was a cagey first half as both sides struggled to create opportunities to score. Mohun Bagan had no shots on target in the opening 45 minutes and they were ineffective in the final third.
In fact, the hosts were being dominated by Aizawl at the centre of the park courtesy of Alfred Jaryan. Interestingly, Joseba Beitia was operating from a deeper position which further complicated matters for Bagan.
Just before the break, Bagan produced a half-chance from a free-kick floated in by Beitia. Aizawl's defence failed to clear which allowed Papa Diawara to set up Tursunov but the Tajik forward ballooned his shot over the crossbar.
Bagan showed more urgency in the second half and started raiding Aizawl's fort with more intent and purpose.
The deadlock was finally broken in the 80th minute with Diawara scoring his 10th goal of the campaign. A brilliant give-and-go between Nongdamba Naorem and Beitia split open Aizawl's defence. The Spaniard then released the former Sevilla striker who rifled a low shot into the net.
The goal was a huge blow for Aizawl who struggled to get back into the game. Bagan stood firm till the final whistle to register an important win that sealed the league title.