"I like to think I've done my part, my little part in history to set us on a better course", Ryan said.
In Wisconsin, the most likely Republican candidate is state Assembly Speaker Robin Vos, multiple Republicans in the state said. "Progressives need to fight as tirelessly on behalf of working people as Speaker Ryan did trying to destroy them", he said.
He will serve out his term until January, when he will not stand for re-election. But Ryan has had a rocky relationship with President Trump, and condemned Trump's more controversial moves on a number of occasions during the campaign.
Ryan told reporters on Capitol Hill, "You realize something when you take this job".
In a brief statement, Pelosi didn't cite any specific issues she wants to tackle with the Republican she has opposed on almost every issue.
It's unlikely that the two sides will compromise on much legislation in an election year. While Trump won the district by 10 points in the 2016 election, Ryan won by 35 points. "Despite our differences, I commend his steadfast commitment to our country", she said.
Ryan, who reluctantly assumed the House leadership in 2015 and never fully embraced President Donald Trump, has given no sign of his future political ambitions. We are with you Paul!'
"I have every confidence I will be handing this gavel on to the next Republican Speaker of the House next year", he said.
In a statement, Stefanik called Ryan "a true friend and mentor".
He said he meant to "run through the tape" in finishing out his term, and he added he believed he would leave in January with the Republican majority intact and with a "very bright future".
"We can all read between the lines", said moderate Republican Rep. Charlie Dent from Pennsylvania.
Brendan Buck, counselor to the speaker, says the "the speaker is proud of all that has been accomplished". "Capping off a remarkable twenty-year career in Congress, Paul's speakership has yielded one signature accomplishment after another for his conference, his constituents in his beloved home state of Wisconsin, and the American people".
Meanwhile, House Majority Leader Kevin McCarthy and Majority Whip Steve Scalise, both Republicans, are expected to fulfill Ryan's position as Speaker.
In the 2012 presidential election, he was the Republican Party nominee for vice president, running alongside former Massachusetts Governor Mitt Romney. More than 30 have announced plans to leave by the beginning of 2019. Ryan had made tax cuts a centerpiece of his legislative agenda, and Congress delivered on that late past year.
Ryan has been serving in Congress since 1999 and has been House Speaker since 2015. Rep. Mark Walker, R-N.C., said an emotional Ryan "choked up a few times trying to get through" his remarks to colleagues and received three standing ovations.