The Dons' goals were all of the highest quality, with McGinn's first-half free-kick and late crisp volley sandwiching fine finishes from Calvin Zola and Michael Hector as Aberdeen moved to within four points of leaders Celtic.
Partick, who have claimed 10 of their 13 points on their travels this season, threatened in spells with Kallum Higginbotham the fulcrum of their attack, but could do nothing to prevent falling to their fifth defeat of the season.
The visitors started well, with Gabriel Piccolo failing to capitalise when Higginbotham's corner found him at the far post, but Aberdeen soon warmed to their task and Partick keeper Scott Fox, celebrating a call-up into Gordon Strachan's Scotland squad, showed his quality to keep out Zola's volley from 12 yards.
However he could do nothing about McGinn's free-kick on 25 minutes, which curled over a disfunctional wall and inside the near post after Jonny Hayes had been fouled by Isaac Osbourne.
Zola then added a second from close range on 38 minutes, capping a slick passing move after McGinn and Peter Pawlett combined down the left-hand side.
Partick again showed some enterprise early on after the break, but their first shot on target did not come until 61 minutes and three minutes later they were 3-0 down, Hector cutting back onto his right foot before rifling home from 25 yards for his first goal for the club since joining on loan from Reading.
Higginbotham's reaction was to hit the bar with an audacious attempt straight from the resulting kick-off and the 24-year-old then saw a powerful drive punched away by Fox, who then had to scramble to claw away deflected effort as Higginbotham continued to lead a one-man charge for the visitors.
But Aberdeen would save the best for last with three minutes remaining, with Hector's charge down the right ending with a perfect cross and McGinn's sweet volley.
There was still time for Hayes to be denied by a wonderful last-ditch tackle from Aaron Taylor-Sinclair, but it mattered not as Derek McInnes' men leapfrogged Motherwell and Inverness into second.