voters in Ohio, Vermont, Rhode Island and Texas put him over the threshold. The triumph came one month after his Super Tuesday coast-to-coast victories gave him an insurmountable lead in the delegate hunt and forced his chief rival, Mitt Romney, to drop out of the race.
"It's a very humbling thing," McCain said of finally clinching the nomination.
McCain was heading to the White House on Wednesday for lunch with President Bush - and an endorsement. The two will make a joint statement afterward.
"The president has said he looks forward to vigorously campaigning for the GOP and tonight it has become clear that the GOP nominee will be Senator John McCain," said White House press secretary Dana Perino. "Of course the president is going to endorse the GOP nominee which is going to be Senator John McCain."
Republicans won't officially nominate McCain until early September at the GOP's national convention in Minneapolis-St. Paul.
Shortly after AP called the race, McCain's chief remaining rival Mike Huckabee withdrew from the race.
In Irving, Texas, former Arkansas governor praised McCain and said: "My commitment to him and the party is to do everything possible to unite our party but more important to unite our country so that we can be the best we can be."
