Keane Lewis-Potter sent Brentford ahead in the second minute of the contest, but Olise levelled the scores before Eberechi Eze made it 2-1 to Roy Hodgson's side late in the first period.
Olise then scored again in the 58th minute, and the victory has moved Palace into 13th position in the table, while Brentford are now 15th, only four points clear of the relegation zone.
Brentford made the perfect start to the contest at Selhurst Park, securing the breakthrough in just the second minute through Lewis-Potter, who poked a cross from Mads Roerslev into the back of the net from close range.
The goal was checked, for more than three minutes, for a possible offside, but it was eventually signalled that Brentford had made the breakthrough.
The response from Palace was positive, with Jordan Ayew testing the reactions of Brentford goalkeeper Mark Flekken before Eze had a strike deflected behind for a corner.
The Eagles managed to level the scores in the 13th minute through Olise, who was on hand to volley an Ayew cross into the back of the net from close range.
Jefferson Lerma then tested Flekken in the 16th minute, before Lewis-Potter had a chance down the other end in the 19th minute, only to fire straight at Eagles goalkeeper Dean Henderson.
The opportunities continued to arrive, with Brentford's Nathan Collins just missing the post with a header in the 28th minute, much to the relief of the scrambling Henderson.
Palace scored their second in the 39th minute of the contest, with Eze racing onto the Brentford box and picking out the bottom corner after the ball had run under Jean-Philippe Mateta's foot.
Brentford almost conceded a third late in the first half when a back pass from Ethan Pinnock put his goalkeeper in trouble, but Flekken just about managed to clear for a corner.
Palace had another chance before the end of the first period, but Lerma's strike from a corner was wide of the post, and the referee brought an entertaining opening 45 minutes to an end shortly after.
The Eagles scored a third in the 58th minute of the contest through Olise, who navigated his way into the Brentford box before picking out the bottom corner with an excellent effort.
Olise came close to scoring a third when he again danced towards the Brentford penalty area before looking to find the corner, but this time, his effort was just wide.
Brentford should have been back in the contest 10 minutes from time, but Neal Maupay's effort hit the crossbar before Yoane Wissa poked the rebound over.
Henderson then made a brilliant save late on to keep out Maupay's effort, with Palace repelling some late pressure to secure all three points in their final match of the year.