Roger Guedes opened the scoring in the final minutes of the first half to give Al Rayyan the lead,cooly slotting past the keeper after beating his man with a lovely bit of skill.
Serbia international Mitrovic then doubled that lead eight minutes after the break by heading in a free-kick.
Muaither never looked like turning things around after that, with Al Rayyan largely keeping control of the game until the final whistle to win their first trophy since 2018.
Speaking after the final, Mitrovic said: “The feeling is amazing. We worked very hard for this. It's been a long season, in the end we reach the final.
"We are so happy, because we put a lot of work and hopefully this is a big push for us in the future. This will give us confidence to win more trophies.
"But I'm very happy for the final. After a long time, we bring a trophy to the club.”
It's the first trophy that Mitrovic has won since arriving in Qatar from Al-Hilal in Saudi Arabia, and comes a month after he outlined that as his biggest goal in an exclusive interview with Flashscore.
“The goal is to win at least one trophy,” he said in March.
“In the last few years, the team has been really unlucky, came close to winning a few trophies but never took them home. So I hope the goals I score will be important in bringing a trophy back to the club."
