The striker, back in the team following a hamstring problem, headed in Danny Simpson's right-wing cross in the dying moments to overcome the lowly visitors.
It was tough on Doncaster, who caused them plenty of problems and led through Theo Robinson's 43rd-minute opener before Matt Phillips equalised.
Phillips' close-range finish ended Rangers' three-match run without a goal and Austin completed the turnaround to take them back up to third in the table.
Rangers had been unimpressive and lost Junior Hoilett to injury after 12 minutes at Loftus Road, where Rovers belied their lowly position - and the wet and windy conditions - with some impressive passing and movement.
Austin had a header from Joey Barton's right-wing cross well saved by goalkeeper Ross Turnbull early on.
And when Simpson's low cross then fell to Niko Kranjcar, the Croatian shot wide of Turnbull's right-hand post.
Doncaster always posed a threat at the other end, with Mark Duffy just failing to connect with Robinson's whipped cross and Richie Wellens shooting narrowly wide after jinking his way into the box.
The visitors' deserved breakthrough came after Yossi Benayoun, making his home debut, shoddily gave the ball away.
He was robbed by Federico Macheda, who sent Robinson through for the forward to fire into the bottom corner.
Rangers, highly fancied to win promotion back to the Premier League at the first attempt, were struggling badly and were booed off at the interval by the frustrated home fans.
Manager Harry Redknapp, who had to persuade QPR's hierarchy to sanction last month's signing of the 33-year-old Israeli, responded by replacing Benayoun with striker Andy Johnson at half-time.
The switch to two up front gave Rangers some attacking impetus, but they needed a defensive lapse to help them draw level 10 minutes into the second period.
An off-balance Luke McCullough was unable to clear Benoit Assou-Ekotto's cross at the far past and in the resulting scramble the ball dropped to Phillips, who poked home.
Rangers continued to press, particularly during a 15-minute spell in which the ball was regularly send into the area towards Austin and Johnson.
When Austin headed wide from Simpson's right-wing cross, Doncaster looked likely to pick up a deserved point.
But after Kranjcar had two efforts saved by Turnbull, Austin netted his 12th goal of the season.