"You realize something when you take this job", Ryan told reporters on Capitol Hill on Wednesday morning.
Governor Scott Walker also released a statement on Ryan's decision.
"The reason I thought he wouldn't make this announcement was because, in effect, when you have the Speaker of the House saying he's not running for re-election, it kind of feels like (he's) running up the white flag.for him to bail right now, it makes it much more hard to raise money, mobilize Congressional campaigns.it's going to feed into the narrative of the 'blue wave.' The narrative becomes self-perpetuating and self-fulfilling".
He continued: "But the truth is it's easy for it to take over everything in your life and you can't just let that happen".
Pennsylvania Republican Representative Ryan Costello said Ryan indicated his decision was a "deeply personal" one, made so he could spend more time with his family and not a reflection of the political challenges Republicans face in November.
The opposition Democratic National Committee chair Tom Perez said Ryans retirement is an indictment of Republican leadership that has failed to provide meaningful results for the American people.
Ryan announced his plans at a closed-door meeting of House Republicans Wednesday morning.
After passage of Ryan's long-sought tax overhaul late previous year, the speaker clashed with President Donald Trump over his planned tariffs. "We are with you Paul!"
The Wisconsin Republican is expected to discuss his decision at a press conference on Wednesday.
Priebus tweeted his praise for Ryan, but didn't say whether he would consider returning to the Wisconsin district where he used to live for a run. Two Democratic challengers are vying for the party's nomination, Bryce and Cathy Myers. When Ryan was chosen, he was considered a compromise candidate to replace John Boehner, who had fallen deeply out of favor with the GOP.
"This is a huge blow for Republicans in Congress", said Sykes on WTMJ. Three factions ended up supporting him, and he became the youngest speaker at age 45 to elected since 1869.
In 2012, Ryan was Mitt Romney's running mate in the presidential election.
Congress was mired in partisan budget talks at the time, approving limited spending appropriations as emergency measures rather than passing a full budget.
Ryan, a Wisconsin Republican, has been in Congress since 1999 and became House speaker in 2015.
Axios was the first to report that Ryan, 48, would leave Congress at the end of his term. Thirty-seven Republican House members are leaving office when their term ends in January 2019. Ryan "recently" came to the conclusion that wasn't the best path for him, one of the sources said.
Ryan touted the passage of the Tax Cuts and Jobs Act he led a year ago, which overhauled the nation's tax system, and the rebuilding of the nation's military as two of his proudest achievements. "That's why we're going to win in November, whether he runs or not". Obama signed it into law later that year.
House Freedom Caucus Chairman Mark Meadows (R-NC) suggested that Ryan may not be able to continue serving as Speaker on Wednesday.
So I will be setting new priorities in my life.
Boehner had encouraged Ryan to seek the position to help unify a fractured party that was threatening to remove Boehner from his position.