The hard-hitting West Indies opener hit nine fours and five sixes to help Bangalore pile up an imposing 185-4 before Daniel Vettori grabbed three wickets to restrict Mumbai to 142-8 in 20 overs at the Chidambaram Stadium.
Gayle, the highest run-getter of the tournament with 608 runs from 11 innings, also shared 113 runs with his young opening partner Mayank Agarwal who made a fine 41 off 31 balls.
Bangalore, losing finalists of the 2009 IPL edition, will now take on Chennai in the title clash at the same venue on Saturday.
"The outfield was very quick and wicket was good to bat on," said Gayle, 31.
"Lasith (Malinga) and Harbhajan (Singh) are their key bowlers so I was looking to be a bit tentative against them. The wicket held up a bit when they chased, so we don't know what to expect in the final."
Mumbai's chase began on a promising note but Bangalore bowlers struck back to reduce them to 89-6 by the 13th over.
After losing opener Aiden Bizzard early, Mumbai promoted Harbhajan Singh up the order at number three but the bold move backfired as he was dismissed by medium-pacer Sreenath Aravind for a seven-ball 13.
Skipper Sachin Tendulkar kept Mumbai in the hunt, mixing caution and aggression during a 40-run effort off 24 balls but his dismissal in the eighth over triggered a batting collapse.
Middle-order batsman Rohit Sharma (13) was caught by Luke Pomersbach off Vettori and two balls later Ambati Rayudu was trapped leg before by the left-arm spinner.
Kieron Pollard's woeful run with the bat continued with the West Indies Twenty20 specialist holing out to Abhimanyu Mithun inches off the boundary ropes for three.
"I thought the way Gayle started, that set the tone for them," said Tendulkar. "We ended up giving 15 runs extra, 170 would have been par. I felt it (reaching the target) was possible, it was within our reach.
"But in the middle overs we got stuck. The middle order I felt could have been more consistent, but it could not happen."
Bangalore set the early pace after being asked to bat first, hammering 27 runs in the first over by paceman Abu Nechim and racing to 67-0 off just five overs.
Gayle reached the 50-run mark with a scorching four over the mid-wicket fence but fell short of a well-deserved century with James Franklin taking a superb running catch off Munaf Patel (2-27) in the 15th over.
Nechim, who gave away 56 runs off his four overs, had something to cheer about when the in-form Virat Kohli played on to his stumps after making just eight.
Patel had Pomersbach caught by Lasith Malinga (four) for his second wicket of the game, the dismissal helping Mumbai pull back the run flow somewhat towards the end of the innings.
Copyright AFP (Agence France-Presse), 2011