John Maginnes, Akio Sadakata and Donnie Hammond finished in a tie for fifth at 14-under-par 418.
Brehaut survived the grueling six-day event contested at PGA West's Nicklaus Tournament Course and Stadium Course to take the top honor. The 39-year-old earned his PGA Tour card for the 2003 season along with 37 of his peers.
'To win this is huge,' said Brehaut. 'Probably the biggest thing I have ever done in my golf career. I'm very proud of that.'
Brehaut came into the final round tied for the lead and struggled early on the Stadium Course with two bogeys over the first three holes. He countered with a birdie at the par-five eighth but faltered again with a bogey at the 12th. Brehaut then collected a birdie at the par-four 15th to secure first place.
'To shoot 73 on this golf course is not that bad especially being in the position where you felt like you wanted to play well but didn't want to mess up,' said Brehaut, who had made it through three previous Q-Schools. 'I was fighting the demons there a little bit.'
Brenden Pappas, Aaron Barber and Brian Bateman earned their PGA Tour cards after they finished tied for eighth at 13-under-par 419.
'I'm very happy right now but it hasn't really hit me because of how stressful that back nine can be,' said Barber. 'I haven't really set any goals for next year because I don't know what to expect.'
Richard Johnson, Dean Wilson, David Sutherland, Scott Laycock, John Morgan and Joel Kribel were one shot further back at 12-under-par 420.
Paul Goydos, Vance Veazey, Mark Wilson and Anthony Painter finished at 11- under-par 421. They were followed by Jeff Klein, Tom Gillis, Bart Bryant, Carl Pettersson and Dave Stockton, Jr. at 10-under-par 422.
Ken Green, a five-time winner on the PGA Tour, shot a final-round 68 to make his way back to the main circuit. Green was joined by Woody Austin, Kenichi Kuboya, Andy Miller, Brett Quigley, Brad Lardon, Jason Caron and Ben Curtis at nine-under-par 423.
'I really can't express what this means,' said Green, who regained his PGA Tour card for the first time since 1996. 'It has been a long struggle. I hung in there and kept fighting.'
Brian Watts, Mike Grob, Cameron Yancey, Mike Heinen and Mathew Goggin finished tied for 34th at eight-under-par 424 to round out the list of those earning PGA Tour cards for 2003.
Casey Martin was in position to gain his card but struggled with a final-round 77 to finish in a tie for 57th at five-under-par 427. Martin was one of many who earned full-exempt status on the 2003 Nationwide Tour.