"I have given this job everything I have," he said. "We're going to have a great record to run on."
But Ryan's impending departure also sets off a scramble among his lieutenants to take the helm.
And it will fuel speculation that Ryan is eyeing a coming Democratic surge, fuelled by opposition to Trump, that could wrest control of the House from Republicans' grip. Several GOP veterans have announced plans to retire in recent months and another, Congressman Dennis Ross of Florida, followed Ryan today.
After talking to Trump, Ryan, 48, first announced his plans at a closed-door meeting of House Republicans.
Moments later, Ryan told reporters that if he were to stay for one more term, his children — now all teens — would only know him as a weekend dad.
"I can't let that happen," he said.
The Speaker had been heading toward this decision since late last year, said a person familiar with his thinking, but as recently as February he had considered running for another term.
His own father died suddenly of a heart attack when he was 16, and though Ryan is in good health, the distance from his family weighed on him. A final decision was made over the two-week congressional recess, which was partly spent on a family holiday in the Czech Republic.
For many Republicans, Ryan has been "a steady force in contrast to the President's more mercurial tone," said Congressman Mark Sanford of South Carolina. "That's needed."
Ryan, from Janesville, Wisconsin, was first elected to Congress in 1998. Along with Eric Cantor and Kevin McCarthy, he branded himself a rising "young gun" in an ageing party and a new breed of hard-charging Republican ready to shrink the size of government.
He became GOP presidential nominee Mitt Romney's running mate in 2012.
Ryan was pulled into the leadership job by the abrupt retirement of Speaker John Boehner in 2015. Boehner had struggled to wrangle the chamber's restless conservative wing and failed to the seal big deals on fiscal policy he sought. Ryan had more trust with the hardliners in the House.
But Ryan ultimately had to wrestle with another unexpected challenge: Trump, a president with little of Ryan's interest in policy detail or ideological purity. The two have had not had a close working relationship.
House Majority Leader McCarthy, a Republican from California known to be tighter with Trump, is expected to again seek the top leadership post that slipped from his reach in 2015. He will likely compete with Majority Whip Steve Scalise of Louisiana.
Ryan's announcement comes as Republicans are bracing for a potential blue wave of voter enthusiasm for Democrats, who need to flip at least 24 GOP-held seats in November to regain the majority.
As the House GOP's top fundraiser, Ryan's sudden lame duck status could send shockwave through donor circles that are relying on his leadership at the helm of the House majority. He has hauled in US$54 million so far this election cycle.
"It injects some more uncertainty to be sure," said the No. 2 Senate Republican, John Cornyn of Texas. "It's just another issue that's floating out there, and obviously there's going to be some competition for his successor."
- AP
