PSG already had one foot in the round of 16 following a convincing 3-0 first-leg victory and were eager to quickly add to their lead here, as Bradley Barcola scuffed a shot into the side netting following some fine work by Ousmane Dembele.
Eric Roy’s men looked to seize their opportunity on the break and came inches away from clawing into the Parisiens’ 3-0 aggregate lead when Marquinhos cleared Pierre Lees-Melou’s effort off the line.
However, the hosts broke the deadlock on the night in the 20th minute, as Barcola latched onto Fabian Ruiz’s superb long-range pass and fired a clinical finish past Gregoire Coudert at the near post.
The hosts were in cruise control from that point, with Brest struggling to cope with the intensity and movement from Luis Enrique’s side.
The hosts doubled their lead through Khvicha Kvaratskhelia’s first Champions League goal for PSG, sliding home at the far post after Barcola guided a Joao Neves cut-back into the Georgian’s path.
It had been a sobering first half for the visitors, but they spurned a golden opportunity to halve the deficit when Gianluigi Donnarumma made a fine save to deny Lees-Melou, but Mama Balde couldn't divert the rebound on target.
Ruiz should have added a goal to add his assist three minutes after the restart, but agonisingly shot wide after being teed up by Dembele in the box.
Roy’s side were keen not to exit the competition with a whimper, as Lees-Melou’s strike cannoned off the post, but it was PSG who added a third through Vitinha.
Ruiz laid the ball off for the Portuguese midfielder to unleash a fine right-footed strike past Coudert.
Substitute Desire Doue added his name to the scoresheet within three minutes of entering the game, after Goncalo Ramos expertly weaved his way past Brendan Chardonnet and laid the ball on a plate for the Frenchman to execute a fine finish.
PSG were in no mood to show mercy to the Brittany outfit and added a fifth when Nuno Mendes had a simple tap-in at the far post from Achraf Hakimi’s ball across the face of goal.
Ramos would add a sixth when Doue turned provider for the forward to apply the deftest of finishes beyond Coudert.
They weren’t done there, and Senny Mayulu provided the final nail in Brest’s Champions League coffin with a close-range finish after being teed up by Kvaratskhelia.
This was a ruthless way for Roy’s side to exit the competition, and they can reflect on a fourth defeat to the reigning champions this season alone - conceding at least three goals on each occasion.
PSG extended their longest unbeaten run against any opponent in their history - now standing at 32 games (W24 D8), and can now look forward to a round-of-16 tie against Liverpool or Barcelona.