McIlroy, 21, the world's ninth-ranked golfer, earned his first U.S. title at this year's Quail Hollow Championship. But he told the BBC he felt lonely on the PGA circuit and wanted to return home.
He said his decision was made last month while helping Europe defeat the United States at the Ryder Cup in Wales.
"There was camaraderie out there and I got to know the European guys better," McIlroy said. "If you're not playing well in the United States then it can be lonely, but over here you have your mates."
The decision has reinforced a feeling that the European circuit is overtaking the PGA as the home to the world's best golfers and demonstrates it's possible to be a dominant force in the game without committing to the American tour, the BBC said.