The Frenchman survived horrendous changeable conditions to cross the line first, in a race where only 10 cars made the finish.
Tech 1 driver Bianchi moved up from fourth to second at the start of the race, taking advantage of a slow start for championship leader Robin Frijns from the front row. But with rain falling the track was already too wet for slick tyres in some places.
Polesitter Kevin Magnussen was the first to fall foul of the conditions, crashing at Becketts on lap two while leading. Bianchi and Frijns took that as a signal and pitted for wets at the end of the lap, leaving Alexander Rossi to lead the race on slicks.
But Rossi's race lasted just a few more corners, as he became the first of seven cars to crash at a flooded Luffield corner on lap three. Other significant runners to join him in the wall were Sam Bird, Marco Sorensen and Nico Muller.
The race had to be red-flagged because there were not enough recovery vehicles to clear the mess. Will Stevens led from the restart, having been allowed to change from slicks to wets during the stoppage.
But on the first racing lap, Stevens spun out, as he was the first car to encounter an awful amount of water on the track at Stowe.
That left Bianchi leading Frijns (Fortec), with series debutant Nigel Melker, who had also gone off at Luffield on lap three but was the only driver to keep going, in third for Lotus.
Nick Yelloly was next up in fourth, and after surviving a bit of an attack from Lucas Foresti and Carlos Huertas, the Briton was able to consolidate his position to the finish.
There were plenty more spinners and crashers further back, but the star of the restarted race was Red Bull junior Antonio Felix da Costa. The Portuguese driver charged through from 13th to fifth by the finish, staying out of trouble and picking off several of his more cautious rivals in the process.
Race one results (20 laps):
1. Jules Bianchi Tech 1 1:03.31.309
2. Robin Frijns Fortec + 7.542
3. Nigel Melker Lotus + 17.372
4. Nick Yelloly Comtec + 27.806
5. Antonio Felix da Costa Arden Caterham + 37.119
6. Carlos Huertas Fortec + 49.121
7. Lucas Foresti DAMS + 52.050
8. Walter Grubmuller P1 + 1:09.383
9. Vittorio Ghirelli Comtec + 1:21.149
10. Daniel Zampieri BVM Target + 1 lap
Retirements:
Marco Sorensen Lotus 25 laps
Nigel Melker Lotus 19 laps
Daniel Zampieri BVM Target 8 laps
Walter Grubmuller P1 6 laps
Kevin Magnussen Carlin 3 laps
Zoel Amberg Pons 0 laps
Yann Cunha Pons 0 laps
Anton Nebylitskiy RFR 0 laps
