Bottom side Barnsley have been woeful at the back so far this season but they defended excellently before Austin scored from close range after being set up by substitute Junior Hoilett on 66 minutes.
And the summer signing sealed Rangers' 2-0 win three minutes from the end, slotting home from the penalty spot after he was tripped in the area by Martin Cranie.
QPR, who are still unbeaten in the Championship and remain second behind leaders Burnley, totally dominated the match.
But they were often frustrated by Barnsley's stubbornness - not least when Richard Dunne's header from Tom Carroll's left-wing corner was cleared off the line by David Perkins.
Jack Butland then came to Barnsley's rescue by producing a fine double save.
Benoit Assou-Ekotto robbed Paddy McCourt and picked out Austin but the striker's effort was kept out by the on-loan goalkeeper, who also blocked Alejandro Faurlin's follow-up.
Bar a misplaced cross from Tom Kennedy which had to be tipped over by Rs goalkeeper Rob Green, Barnsley hardly threatened before appealing in vain for a penalty two minutes before half-time.
As Rangers struggled to clear their lines the ball struck Niko Kranjcar's hand but the Croatian was given the benefit of the doubt by the referee.
The decision angered Barnsley manager David Flitcroft, who clearly felt a spot-kick should have been awarded.
Flitcroft could certainly do with a change of fortune - his side have taken only five points from their 11 league matches so far this season and have lost all six of their away games.
They continued to defend doggedly after the break and Rangers were denied by another goal-line clearance, this time when Krancjar's shot was scooped over the bar by McCourt.
But Rangers kept pressing and Austin's cool finish finally broke the deadlock.
Shortly after coming on, Hoilett tricked his way towards the left-hand touchline and pulled the ball back for the former Burnley man, who netted from seven yards out.
After a slow start to his QPR career, Austin's late penalty means he has now scored five goals in as many matches for Harry Redknapp's team.
Yet he was almost upstaged by recent signing Javier Chevanton, who sent a blistering injury-time effort just over the bar after coming off the bench for his debut.