On Monday, midfielder Motin Mia put the Kings into the lead in the 29th minute.
But Kings received a jolt just eight minutes later when their defender Yeasin Arafat was shown a red card.
After getting reduced to 10 men, Kings fought hard to maintain their 1-0 lead, focusing more on defence then attack.
But all their fears got dispelled in the 81st minute when super sub Biplo Ahmed, who replaced Motin Mia, netted the second goal for the Kings, pretty much sealing the match for the defending champions.
Soon after the final whistle, the players and officials of the Kings started celebrating on the field.
This was the second consecutive victory for the Kings against Saif. They beat Saif 4-3 earlier in the league.
The Kings were crowned champions after securing 51 points from 20 matches with 16 wins, three draws and one loss.
Independence Cup and Federation Cup champions Dhaka Abahani have 41 points from 19 matches, 10 points behind the league leader Kings.
The Kings will play the remaining two league matches against Dhaka Abahani on 24 July and Sheikh Jamal DC on 30 July, the results of which will not affect their place in the points table.