Piastri makes it four F2 poles in a row in Saudi Arabia
Shwartzman had the edge over his teammate up until the final run in qualifying at the all-new Jeddah Corniche Circuit.
The Russian driver took to the top of the timesheets after the initial runs, less than a thousandth clear of Theo Pourchaire.
Pourchaire took provisional pole position at the chequered flag, but was quickly beaten by Piastri, whose outstanding first sector handed him a 0.3s margin.
Shwartzman was on course for his maiden F2 pole position but a small mistake at the final corner meant he had to settle for second.
Piastri - who was announced as Alpine’s official reserve and test driver for 2022 in November after missing out on a full-time drive with Alfa Romeo - will start Sunday’s feature race from pole; he will line up 10th on the grid for the first reserve sprint race.
It’s a front-row lockout for Prema as it looks to secure another teams’ title.
Behind the Prema duo was Pourchaire, while Christian Lundgaard made it two ARTs in the top four in qualifying.
Felipe Drugovich qualified fifth ahead of title contender Guanyu Zhou - who will drive for Alfa Romeo in F1 next year.
Zhou now trails Piastri by 40 points in the title race going into the final rounds of the campaign.
Completing the top 10 was: Ralph Boschung, Juri Vips, Marcus Armstrong and Liam Lawson.
On his debut in F2, Clément Novalak was a respectable 12th for MP Motorsport.
Dan Ticktum’s qualifying was ruined by a puncture on his final run, leaving him 13th.
2021 F3 runner-up Jack Doohan qualified 16th, while Olli Caldwell was 19th in the Campos.
Logan Sargeant is the final F3 graduate as he qualified 21st, recovering from a shunt in practice.
Click here for the full Formula 2 qualifying results from Jeddah