The Argentinian lined up fourth for Saturday’s sprint race, with the start delayed by 10 minutes as rain began to fall, though all of the field bar Gregoire Saucy (ART) stuck with slick tyres.
Colapinto took third at Village on lap one as team-mate Jonny Edgar fell back off the line as poleman Sebastian Montoya (Hitech) held the lead from Jenzer driver Taylor Barnard.
Williams junior Colapinto held onto third during the safety car, prompted by heavier rainfall, and took the lead after contact between Barnard and Montoya on the restart.
From there, he built a strong lead to take his first win since Monza last year, with championship leader Gabriel Bortoleto in second for Trident and Campos’ Christian Mansell scoring his maiden podium in third.
Red Bull junior Montoya held the lead off the line, with Barnard in second as Edgar fell back to third.
He was soon passed by Colapinto before Hitech driver Luke Browning took fourth into Stowe and team-mate Gabriele Mini followed him through at the final corner.
Edgar continued to fall down the order, settling for 10th heading into lap three.
The rain, which had eased, started again on lap five, with Barnard now within DRS of Montoya with another 0.6s back to Colapinto.
Heavier rain came three laps later, with DRS disabled before the safety car was deployed.
The change in conditions prompted several drivers to dive into the pits, with Prema driver Dino Beganovic, who had climbed to 20th from the back of the grid after an engine issue in qualifying, first to stop.
Several others, including the other two Prema drivers Zak O’Sullivan and Paul Aron, Luke Browning and Pepe Marti (Campos) stopped next time round as the rain continued.
Source: Autosport