House Speaker Paul Ryan is not seeking re-election and will retire from Congress after this year, the Wisconsin Republican announced Wednesday.

"You realize something when you take this job," Ryan told reporters on Capitol Hill on Wednesday morning. "It's a big job with a lot riding on you ... but you also know this is not a job that does not last forever. ... You realize you hold the office for just a small part of our history. So you better make the most of it."

He reminded reporters that he took the job "reluctantly" in 2015, when he took over from John Boehner, but Ryan also said he has no "regrets."

"I like to think I've done my part," he said.

Ryan's departure is a blow to GOP members who saw the Wisconsin Republican as a stable and policy-oriented leader in a party shaken by the tumultuous Donald Trump presidency. He has been a fundraising juggernaut ahead of the midterms this fall, and helped translate GOP agenda items into legislation such as a series of tax cuts and rolling back banking legislation put in place under Democrats.

In his prepared remarks, Ryan focused on the tax law that passed last year as a key legacy he left behind and spoke at length about his desire to go home to Wisconsin to be home with his family. He said that the 2018 midterms and the chance that he wouldn't be speaker didn't factor at all into his decision to announce his retirement.

"None whatsoever actually," Ryan said.

Trump, who has at times fought with congressional Republican including Ryan, tweeted praise for the speaker after his announcement.

"Speaker Paul Ryan is a truly good man, and while he will not be seeking re-election, he will leave a legacy of achievement that nobody can question. We are with you Paul!" Trump wrote.

Ryan wants to spend time with his family

According to two sources with direct knowledge, in calls this morning with his leadership team, Ryan made clear much of this decision was about spending time with his family, but also noted that he planned to leave after this Congress and didn't think it was fair to his district or the GOP conference to run for re-election only to leave right after. Sources familiar told CNN that Ryan called House Majority Leader Kevin McCarthy and Majority Whip Steve Scalise about his retirement before the news broke.

Ryan called Trump and Vice President Mike Pence on Wednesday morning ahead of his announcement, a source familiar with their conversation told CNN.

The speaker met with members of his caucus on Wednesday morning. Rep. Darrell Issa of California told CNN that Ryan told members he promises to be more than a "Sunday dad" and he cited his family as part of his decision. At one point Wednesday morning, reporters outside the conference room could hear a long applause from inside the meeting.

Ryan, a Wisconsin Republican, has been in Congress since 1999 and became House speaker in 2015. Ryan reluctantly ran to replace then-Speaker Boehner of Ohio, who retired after sparring regularly with the most conservative members of his conference, including many members of the House Freedom Caucus.

Some of Ryan's close friends previously told CNN that he might leave office after the 2018 midterms. Ryan said in a January interview with CBS News that re-election was a decision he and his wife were planning to make together in late spring, and in March he denied a rumor that he wouldn't seek re-election.

The news of Ryan's retirement was first reported by Axios.

Who will replace Ryan?

While it has long been expected that Ryan would leave after the 115th Congress, sources close to him have said for weeks they expected he would run again in order to raise money for the party and not throw his conference into a leadership battle. Ryan "recently" came to the conclusion that wasn't the best path for him, one of the sources said.

McCarthy and Scalise of Louisiana are among the contenders congressional observers see as most likely to replace Ryan.

Scalise demurred when asked if he would run for the speakership.

"We're getting way ahead of ourselves. Obviously, there's a lot of speculation, but I've been real clear for a long time, I don't want to get into speculation," he told Fox News, adding, "We've got to make sure we keep the majority."

Scalise told Politico in March that he would not rule out running for the speakership if Ryan were to retire.

One source with the conservative bloc, the House Freedom Caucus, says McCarthy is, at this early stage, likely to have the support to become the next Speaker with the group's chairman Rep. Mark Meadows a front-runner to become Majority Leader.

Meadows, of North Carolina, praised Ryan's tenure in a statement after the news broke.

"Speaker Ryan has served our country well for decades as a thoughtful policy leader in the House," he told CNN. "He will be successful in any future endeavor and I wish him all the best."

McCarthy had previously run to succeed Boehner in fall 2015, before abruptly dropping out, leaving space for Ryan to run and be elected at the end of October that year.