Trump chose Schaeffer, a California-born attorney, over James Sun, 29, an Internet entrepreneur from Seattle. The season finale of "The Apprentice: Los Angeles" aired live Sunday from the Hollywood Bowl.
"James, you're fired. Stefani, you're hired," Trump said.
Schaeffer, 32, was cool under pressure as she made her final pitch to the real-estate mogul.
"I was never under fire in the boardroom," she said. "Not once did you ever see me brought back by any team members, nor did you ever hear a negative word spoken about me from day one of this process."
"That's largely true," Trump replied.
Schaeffer had the choice of working on Trump's new resort development in the Caribbean or a condo project in Atlanta. She chose the Caribbean.
The previous five seasons of "The Apprentice" were set in Manhattan.