GETTYSBURG, Pa.—Rick Santorum suspended his campaign for the White House on Tuesday, clearing the way for former Massachusetts Gov. Mitt Romney to claim the Republican presidential nomination and end the primary season after three months and 37 contests.

The former Pennsylvania senator told a news conference he had made the decision over the weekend with his family. Trailing far behind Mr. Romney in the delegate count, Mr. Santorum faced a growing chorus of calls from within his party to exit the race and allow Republicans...