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.
He 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 slowed, 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, Browning and Pepe Marti (Campos) stopped next time round as the rain continued.
The safety car period ended on lap 13 as the rain slowed, with Barnard attempting a move on Montoya into Turn 1, catching his rear and sending him into a spin, falling to 18th, while Barnard suffered a puncture.
This handed Colapinto the lead, with Bortoleto in second and Barnard clinging onto third, though he soon dropped down the order as the puncture took effect.
Those who had stopped began to make good progress, with Beganovic and Aron benefiting the most as the Estonian ran as high as sixth.
But it wasn't to last, as a drying track saw those on slicks again benefit, allowing Mini to reclaim fifth from Aron as Hugh Barter (Campos) did the same.
Caio Collet finished fourth for Van Amersfoort Racing ahead of Mini and Barber, with Sunday polesitter Leonardo Fornaroli in seventh for Trident.
Montoya climbed back to eighth after the contact from Barnard, with Ido Cohen in ninth for Carlin and Aron rounding off the top 10.
| Cla | Driver | Team | Gap |
|---|---|---|---|
| 1 |
 Franco Colapinto |
 MP Motorsport |
|
| 2 | Gabriel Bortoleto |  Trident |
3.700 |
| 3 | Christian Mansell |  Campos Racing |
5.800 |
| 4 |
 Caio Collet |
Van Amersfoort Racing |
6.200 |
| 5 | Gabriele Minì | Hitech Pulse-Eight | 14.500 |
| 6 | Hugh Barter | Campos Racing |
17.400 |
| 7 | Leonardo Fornaroli | Trident |
19.600 |
| 8 |
 Sebastian Montoya |
Hitech Pulse-Eight | 23.600 |
| 9 |
 Ido Cohen |
Rodin Carlin | 42.000 |
| 10 | Pepe Martí | Campos Racing |
52.700 |
| 11 | Alex Garcia |  Jenzer Motorsport |
52.800 |
| 12 | Paul Aron | Prema Powerteam |
53.300 |
| 13 | Dino Beganovic | Prema Powerteam |
54.200 |
| 14 | Luke Browning | Hitech Pulse-Eight | 54.800 |
| 15 | Nikola Tsolov |  ART Grand Prix |
55.900 |
| 16 |
 Zak O'Sullivan |
Prema Powerteam |
57.400 |
| 17 | Oliver Goethe | Trident |
58.300 |
| 18 | Nikita Bedrin | Jenzer Motorsport |
1'01.400 |
| 19 |
 Sophia Flörsch |
PHM Racing by Charouz | 1'07.700 |
| 20 |
 Rafael Villagomez |
Van Amersfoort Racing |
1'08.800 |
| 21 | Mari Boya | MP Motorsport |
1'11.000 |
| 22 | Oliver Gray | Rodin Carlin | 1'11.600 |
| 23 |
Gregoire Saucy |
ART Grand Prix |
1'11.700 |
| 24 |
 Kaylen Frederick |
ART Grand Prix |
1'13.900 |
| 25 | McKenzy Cresswell | PHM Racing by Charouz | 1'14.900 |
| 26 | Max Esterson | Rodin Carlin | 1'16.400 |
| 27 | Roberto Faria | PHM Racing by Charouz | 1'27.000 |
| 28 | Tommy Smith | Van Amersfoort Racing |
1'31.900 |
| 29 |
Jonny Edgar |
MP Motorsport |
1'43.000 |
| 30 | Taylor Barnard | Jenzer Motorsport |
1'50.600 |
| View full results | |||
