Republican Kevin McCarthy was elected House speaker after 14 failed attempts to win the chamber’s top job and days of grueling negotiations that turned detractors in his favor.

The election marked a personal achievement for Mr. McCarthy, 57, who has pursued the speakership for nearly as long as he has been in the House and had failed to secure the speakership more than seven years ago. It puts him in control of the GOP's only power center in a divided capital.

He made significant concessions in order to bring on board his opponents. Those concessions could lead to gridlock in the relationship between the GOP-controlled House and the Democrat-run Senate, complicating proceedings on his own House floor. In addition, they would make it easier to topple him from the post if members are unhappy.

The House hasn’t had this many failed votes to decide on a speaker since before the Civil War, when it took 44 attempts. This year’s vote was the first time in 100 years that a speaker didn’t win on the first ballot.

To win the job, Mr. McCarthy agreed to restore a rule allowing a single member to call a snap vote on ousting the speaker. The concessions also include commitments to tie spending cuts to a debt-ceiling increase and to a process making it easier to amend individual spending bills, according to several negotiators and people familiar with the talks. And they include a goal of putting more members of the conservative House Freedom Caucus on key committees, including the Rules Committee, which for years has written rules to block amendments from coming up on the House floor.

“I ran out of things to ask for,” Republican Rep. Matt Gaetz of Florida told reporters after he, along with the other five remaining detractors, voted “present” rather than against Mr. McCarthy on the 15th and final ballot. The move lowered the threshold required for Mr. McCarthy to be elected, capturing the speakership with 216 votes, rather than the 218 normally required.

Some of Mr. McCarthy’s allies lamented that his concessions gave away too much of his power and will make it harder for him to govern the House’s fractious GOP caucus.