Romero has struggled for form since winning the 2008 Zurich Classic of New Orleans and has slumped to 837th in the world rankings, but he can now look forward to a healthy European Tour exemption after his outstanding final round at the Golfclub Munchen Eichenried.
"This is a moment that changes my life", the 36-year-old said.
But Romero composed himself to rattle in the birdie chance which gave him the outright clubhouse lead ahead of Detry, who had stormed to the turn in 31 but missed a number of crucial chances on the back nine as he closed with a 66.
It all came down to a four-way battle between Romero, Masters Tournament champion Sergio Garcia, Richard Bland and Thomas Detry.
Bland and Garcia fell back with late bogeys, meaning that they both needed an eagle on the 72nd hole to force a playoff with Romero.
Both are bidding for their first European Tour title.
Garcia narrowly failed to chip in with his third shot, before Bland's 15-foot eagle putt slid past the right edge to confirm Romero's unlikely victory.
"Got my feet wet and holed a second shot into 13".
"A good, solid day", said Garcia, who is going for his third title of the season. "With no status, he's neither here on the European Tour nor the PGA Tour - to go out and shoot 65 today, I'm happy for him and we'll just keep trying".
The overnight leaders started slowly, with Bland playing his first eight holes in one over, while Spaniard Garcia was even par.
Swede Rikard Karlberg finished at 14 under, a shot clear of England's Tommy Fleetwood and Italian Renato Paratore, with Open champion Henrik Stenson six shots behind the victor. "I've not been playing that great".