Here's what you need to know about the fast-rising McCarthy:
Name: Kevin Owen McCarthy
Hometown: Bakersfield, Calif., about 112 miles northeast of Los Angeles. McCarthy is the first Republican in his family.
Birth date: Jan. 26, 1965 (He's 50 years old.)
Notable childhood moments: As a teenager, McCarthy won $5,000 in a lottery. He invested the money in the stock market and opened up a deli at age 19 — "Subway before there was Subway," he once told the National Review. He and his father, an assistant fire chief, built the counter in their garage.
McCarthy credits those years as a small business owner with enshrining in him Republican values, even as his parents are Democrats.
"And I soon learned, if you're a small business owner, you're the first one to work, the last to leave, the last to be paid," he told Fox News's Chris Wallace in a 2014 interview. "You learn what regulation does to your business and the challenges. You wonder where common sense is."
Nonpolitical résumé: After selling the deli to pay his way through college, McCarthy earned his MBA at California State University at Bakersfield. He pretty much jumped into politics right after that.
Political résumé: McCarthy was once turned down for an internship with his local congressman. But he soon began a rapid ascent in politics. He was a state assemblyman in 2002, where he was elected Republican floor leader in his first term. He ran for Congress in 2006, winning the Republican primary and subsequent general election to represent the heavily Republican district that encompasses his hometown.
McCarthy has won every election since, running virtually unopposed in the primary and always winning with at least 70 percent of the vote, even when redistricting before the 2012 election shook up (and changed the number of) his district.
He now represents California's 23rd district.
Current title: House majority leader
Although duties for this job can vary, McCarthy is in charge of the legislative calendar for the House of Representatives. He's also the point person for all 247 House Republicans' concerns, complaints and requests. As the official Republican leader, McCarthy also works closely with Democratic House Minority Leader Nancy Pelosi (D-Calif.).
Twitter handle: @GOPLeader
He tweeted this picture of a prayer with Pope Francis on Thursday:
How he got to the No. 2 slot: Pretty much ever since arriving in Congress in 2007, McCarthy has been climbing the ranks of Republican leadership. In fact, when he became majority leader, he earned the distinction of being the fastest-rising majority leader — or any party leader — in at least a century. He had been in Congress for just four terms.
When House Republicans gained control of the House in the 2010 midterm elections, McCarthy's fellow Republicans elected him in a secret ballot to be their No. 3 leader, called House majority whip. As whip, McCarthy was the guy in charge of making sure every — or at least enough — Republicans voted the way leadership wanted them to.
In 2014, Republicans' No. 2, House Majority Leader Eric Cantor (Va.), lost a stunning primary to tea party candidate Dave Brat. With Cantor out, McCarthy won another secret ballot to take his place, without much fuss.
"I make one promise: I will work every single day to make sure this conference has the courage to lead, with the wisdom to listen," McCarthy told Fox News's Wallace as he ascended to his new leadership position.
Voting record and rundown of the issues: If tea party Republicans think they're going to replace Boehner with one of their own, it's surely not McCarthy.
Prior to becoming majority whip in 2011, his record was among the more conservative Republicans in the House. But being in leadership the last four-plus years has put McCarthy much more toward the moderate/establishment wing of the party.
The conservative Club for Growth gives him a lifetime score of 73 percent, but just 43 percent in 2014. McCarthy is supportive of one of Club for Growth's biggest issues: He has said he does not support renewing the Export-Import Bank, an independent government agency that helps U.S. companies do risky-ish business abroad. Tea party conservatives have decried the bank, which often supports big businesses like Boeing and Caterpillar, for "crony capitalism." He also signed a pledge in 2010 to avoid raising taxes to combat climate change.
At the height of the immigration reform debate in 2014, McCarthy, whose district is 35 percent Latino, said he'd support giving some sort of legal status to undocumented immigrants, but he stopped short of saying he'd support a new path to citizenship.
"The principles aren't written yet, but in my personal belief, I think it'll go with legal status that will allow you to work and pay taxes," he told local Bakersfield TV stations KBAX and KBFX.
McCarthy is also a staunch anti-abortion-rights advocate. Most recently, he voted to cut some $500 million in federal funds for Planned Parenthood after a controversy with the organization's use of fetal tissue. (Planned Parenthood officials deny they did anything wrong.)
Reputation among Republicans: McCarthy helped writers for Netflix's "House of Cards" develop Kevin Spacey's character, Frank Underwood (he let Spacey shadow him). But he promises he's nothing like Spacey's murderous, manipulating character. And if his reputation on the Hill is any indication, that would seem to be true.
McCarthy is known for being a down-to-earth, congenial guy. He sleeps on a sofa in his office because he doesn't want "to feel comfortable in Washington." He remembers details about his fellow lawmakers' families. He hosts tea party conservatives and establishment Republicans for Chick-fil-A and movie nights.
He even plays pranks on his friends; he once called now-Sen. Dean Heller's (R-Nev.) House office pretending to be the Capitol Police concerned about a giant elk head Heller's staff was having trouble fitting through his office door:
"I said, 'I'm from the Capitol Police, and I need to talk to Rep. Heller about what's out there,' " he said in a 2014 interview. "'That is an emergency problem, being out in the hallway. It's detrimental to people's health. Where is this congressman?' They ran and they got him on the phone before they ever realized it was me."
Likelihood of becoming speaker: It's not clear who might give McCarthy a serious challenge at this point, and Boehner, in his resignation press conference, assured that McCarthy would make a good speaker and spoke about him as if he would become speaker.
Pros for being speaker: As noted above, McCarthy is well-liked among Republicans, which has helped him rise so high so quickly.
Cons for being speaker: "Many believe he lacks the political and tactical gravitas to be a force in the House," note The Washington Post's Mike DeBonis and Paul Kane.
Basically, McCarthy is likeable, but many on the Hill wonder if he's tough enough to handle an unruly caucus of about 30 tea party lawmakers — the same lawmakers who threatened to oust Speaker Boehner. Assuming his colleagues elect him to the top post, time will tell.
How he's handling all the attention right now:
Here's a clip from C-SPAN of reporters chasing down McCarthy on Friday morning.
And here's his laudatory statement on Boehner's exit:
“Since I first came to Congress in 2007, John has been serving his constituents and his country with unparalleled passion. John has been a leader, mentor, and most of all friend throughout, and I learned not only from his experience but also from his unshakeable faith and principles. It takes profound humility to step down from a position of power, and John’s depth of character is unmatched.
“As our country has weathered difficult times at home and abroad, John has acted as a true statesman, always moving forward with the best interests of the American people close to his heart. He will be missed because there is simply no one else like him.
“Now is the time for our conference to focus on healing and unifying to face the challenges ahead and always do what is best for the American people.”
This post was updated at 1:23 p.m.