Gayle (75no) and Pollard added 65 off 25 balls as the Windies racked up 205-4, the highest score of the tournament.
Despite a defiant 29-ball 63 from captain George Bailey, Australia never recovered from a poor start, crumbling to 131 all out to lose by 74 runs.
West Indies will meet hosts Sri Lanka in the final in Colombo on Sunday.
It was a phenomenal display from West Indies, based around another show-stopping performance by Gayle.
Despite facing only 41 balls in the innings, the left-handed opener still managed to get within 25 runs of a century, smashing six sixes and five fours with a strike rate of 182.
Marlon Samuels helped set the tempo with a breezy 26 and Darren Bravo hit three towering sixes in his 37 off 31 balls.
However, it was Gayle and Pollard, who plundered 63 runs off the last four overs, who really demoralised Australia.
After watching the previously economical Mitchell Starc get carted for 17 in the penultimate over, Bailey took a gamble by throwing the ball to left-arm spinner Xavier Doherty.
It proved a costly mistake as Gayle heaved a six over midwicket before Pollard helped himself to three maximums in a row.
He holed out at long-off off the last ball of the innings to fall for 38 off 15 deliveries, but the damage had been done.
Australia’s best chance of joining their women’s team in the final was always likely to lie with their prolific openers David Warner and Shane Watson.
So when both were clean bowled by leg-spinner Samuel Badree for single-figure scores inside the first five overs, the writing was all but on the wall.
Warner was dismissed off the last ball of the first over when a television replay confirmed that a googly had shaved his off stump and dislodged the bails.
And, after Mike Hussey had top-edged a return catch to Marlon Samuels following a quickfire 18, Watson was castled for seven by one that fizzed on.
Ravi Rampaul then took two wickets in three balls to have Cameron White caught down the leg side and David Hussey caught and bowled off a leading edge as the Aussies slumped to 42-5.
Bailey, not renowned for his ball-striking, led a one-man counter-attack in a blistering 63 off 29 balls, but with the run rate required creeping above 14 per over, his innings was always likely to be a footnote to proceedings.
And so it proved as Pollard removed Pat Cummins and Bailey in the same over, Brad Hogg was stumped off Sunil Narine and Rampaul bowled Starc to wrap up a phenomenal win.
The Windies are through to their first global final since 2004, when they beat England at The Oval to win the Champions Trophy.
