The jockeying among Republicans in the House for Ryan's seat had already begun.
Ryan achieved his long-held goal of overhauling the USA tax code in December.
Ryan to addressed his decision in a closed-door Republican Party meeting on Wednesday, sources told CNN.
House Speaker Paul Ryan will not run for reelection in November and retire from Congress at the end of his term, the speaker announced Wednesday.
"He's got young kids, and I don't think people realize how hard my job is and look at his job, which must be five times more time consuming", Grothman said.
Ryan (R-Wis.) told colleagues Wednesday that he will not seek reelection this year, ending a almost 20-year tenure in Congress and adding further uncertainty about whether embattled Republicans can maintain control of the House.
Ryan announced Wednesday morning that he will serve out the remainder of his term and retire in January.
Brendan Buck, counselor to the speaker, says the "the speaker is proud of all that has been accomplished".
He had long championed tax reform, a goal accomplished with the passage a year ago of the sweeping GOP tax bill. Following the enacting of the massive tax law, rumours began swirling that Ryan may not run again.
Reports of Ryan's departure have circulated for months.
More than three dozen House Republicans have said they are retiring, or running for another office, or resigning. Ryan was previously chairman of the House Ways and Means Committee and before that chairman of the House Budget Committee. He was former presidential candidate Mitt Romney's running mate for the 2012 election. He was elected House speaker in 2015 after former House speaker John Boehner retired.
He ultimately had to wrestle with another unexpected challenge: President Donald Trump, a president with little of Ryan's interest in policy detail or ideological purity. We are with you Paul!
"Speaker Ryan is a good man who is always true to his word". This is a developing story and we will update it as more information comes.