The former House speaker has defeated former Massachusetts Gov. Mitt Romney to gain the victory in a dramatic turnaround from his earlier, poor showings in Iowa and New Hampshire.
Florida holds the next GOP contest on Jan. 31.
ABC News has projected that former Massachusetts Gov. Mitt Romney will come in second place, former Pennsylvania Sen. Rick Santorum in third, and Texas Rep. Ron Paul in fourth.
Romney, who delivered his speech just after 8 p.m. ET on Saturday night, said: “This race is getting to be even more interesting…This is a hard fight because there’s so much worth fighting for.”