Willett shot a final-round 73 for an 11-under total of 277 to finish with a share of the lead with Fraser, who shot a last-day 71 in rainy conditions on the Gut Larcenhof course.
Willett then sealed his first tour win in 106 starts at the fourth extra hole with a par when Fraser bogeyed.
Both players started the playoff with pars on the first and bogeys on the second before again shooting par on the third.
All four have won since turning pro with McIlroy also winning the U.S. Open last year.
The winning 2007 United States team included Webb Simpson, who won this year's U.S. Open, along with Dustin Johnson, recent winner of the FedEx St. Jude Classic, and Rickie Fowler, who broke through for his first PGA Tour win in last month's Wells Fargo Championship where he beat McIlroy in a playoff.
"I was thinking that only this morning that there are now only just a handful of players from that 2007 Walker Cup who haven't won," Willett said. "You look at the strength of those two teams with the likes of Rory, Webb Simpson, Dustin Johnson and Rickie.
"But to now join the likes of those guys as a tour winner is fabulous, and it's a big weight off my shoulders."
Willett is the ninth first-time winner on the European Tour this year and the 22nd different champion in the 24-year history of the BMW International Open.
"It just feels brilliant to win as this is what you look for growing up as a kid," Willett said. "It took a little while longer than I had hoped, but it's been a bit of a rough ride the past few months, but I'm now back to full health.
"It was a tough day what with the rain and win, and to finish 11 under and to get into a playoff was good. I have been in contention a number of times, including second to (Martin) Kaymer in 2010 at the Dunhill Links, so to polish it off is a great feeling."
McGinley shot the best final-round score of 66 to secure his third top 10 in eight starts this year.