The 21-year-old secured his maiden pole position after hitting the top of the times mid-way through the session with a lap that was just enough to keep him ahead of Brendon Hartley, who was on a charge at the end of the half hour.
Turvey originally took the pole by more than two tenths of a second but Hartley reduced the advantage to 0.086 with a late effort. The Kiwi was then three tenths up on Turvey two thirds of the way round his last lap of the session, but lost a stack of time in the last sector.
Hartley still completes an all-Carlin Motorsport front row, though, and Jaime Alguersuari and Sam Abay made it a 1-2-3-4 for the team.
Marcus Ericsson was fifth fastest for Fortec Motorsport, with Double R teammates John Martin and Atte Mustonen sixth and seventh - Mustonen trying making up for the ground he lost in the morning when he crashed on his out-lap in first practice.
Michael Devaney (Ultimate Motorsport) was the first of the Mygales in eighth, ahead of Nick Tandy's similar JTR car and joint championship leader Sergio Perez completed the top ten for T-Sport.
Guest racer Daniel Campos-Hull was 11th, with Jay Bridger leading the National Class runners in 14th place. Oliver Oakes qualified 16th on his return to the series, while Basil Shaaban - Campos Hull's HBR Motorsport teammate - qualified 23rd for his first outing in British F3 since 2006.
The second qualifying session will take place on Friday morning, with one race that afternoon and the second on Saturday ahead of the start of the FIA GT Spa 24 Hours.
Pos Driver Team Car Time Gap 1. Oliver Turvey Carlin D/M 2:15.361 2. Brendon Hartley Carlin D/M 2:15.447 +0.086 3. Jaime Alguersuari Carlin D/M 2:15.596 +0.235 4. Sam Abay Carlin D/M 2:15.823 +0.462 5. Marcus Ericsson Fortec D/M 2:16.194 +0.833 6. John Martin Double R D/M 2:16.222 +0.861 7. Atte Mustonen Double R D/M 2:16.291 +0.930 8. Michael Devaney Ultimate M/M 2:16.443 +1.082 9. Nick Tandy JTR M/M 2:16.446 +1.085 10. Sergio Perez T-Sport D/H 2:16.592 +1.231 11. Daniel Campos-Hull HBR D/M 2:16.629 +1.268 12. Sebastian Hohenthal Fortec D/M 2:16.788 +1.427 13. Walter Grubmuller Hitech D/M 2:16.821 +1.460 14. Jay Bridger Fluid (N) D/H 2:16.952 +1.591 15. Max Chilton Hitech D/M 2:17.013 +1.652 16. Oliver Oakes Eurotek D/M 2:17.261 +1.900 17. Henry Arundel Double R D/M 2:17.333 +1.972 18. Phillip Major Fortec D/M 2:17.345 +1.984 19. Alastair Jackson Ultimate M/M 2:17.571 +2.210 20. Ricardo Teixeira Ultimate M/M 2:17.723 +2.362 21. Salman Al-Khalifa T-Sport (N) D/H 2:17.784 +2.423 22. Steven Guerrero T-Sport (N) D/H 2:18.224 +2.863 23. Basil Shaaban HBR D/M 2:18.250 +2.889 24. Stefan Wilson Fluid (N) D/H 2:18.490 +3.129 25. Hywel Lloyd CF (N) D/H 2:18.728 +3.367 26. Kristjan Einar Carlin (N) D/H 2:19.047 +3.686 27. Craig Reiff Nexa (N) D/H 2:21.587 +6.226