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Paul Ryan.
"This is the most incredible political feat I've seen in my lifetime," Ryan said.
The Wisconsin Republican had clashed with Trump at times throughout the primary and general election season, but ultimately endorsed him and stuck with it.
"Donald Trump heard a voice out in this country that no one else heard," Ryan said. "He connected in ways with people that no one else did. And now, Donald Trump will lead a unified Republican government."
Ryan praised Trump for setting "the perfect tone last night" in his post-election speech, adding that Trump "earned a mandate" with his victory.
The House speaker said he "didn't think" Trump could win in Wisconsin.
Ryan called for healing the divisions after the bruising campaign, saying he is sure Trump, President Barack Obama, and Democratic nominee Hillary Clinton are all committed to doing so.
The Associated Press declared Trump the president-elect at 2:30 a.m. ET, shortly after the wire service placed Wisconsin in his column.
Trump's victory was one of the most stunning political upsets in history. Clinton was strongly favored to emerge as the victor on Tuesday night, with some analysts estimating Trump's odds of winning the election as low as 1%.