WASHINGTON — Scott Pruitt, the former Oklahoma attorney general who relentlessly pursued President Trump’s promises of deregulation at the Environmental Protection Agency, resigned Thursday after controversies over his lavish spending, ethical lapses, and controversial management decisions eroded the president’s confidence.

Pruitt’s reputation as a dogged deregulator and outspoken booster of the president allowed him to weather ethics scandals in recent months, including questions about taxpayer-funded first-class travel, a discounted condominium rental from the wife of a District of Columbia lobbyist, and the installation of a $43,000 soundproof phone booth in his office.

But revelations about his behavior continued to mount, including reports that he repeatedly enlisted subordinates to help him search for housing, book personal travel, and help search for a six-figure job for his wife. That quest included setting up a call with Chick-fil-A executives in which he discussed his wife’s becoming a franchisee, as well as outreach to a conservative judicial group that eventually hired Marlyn Pruitt.

In recent weeks, an exodus of trusted staff members left Pruitt increasingly isolated, and some Republican lawmakers wearied of defending him. Investigators on Capitol Hill had summoned current and former EPA aides for questioning as part of more than a dozen federal inquiries into Pruitt’s spending and management of the agency.

On Thursday the White House informed Pruitt that he had to submit his resignation, according to two individuals who spoke on the condition of anonymity because of the sensitivity of the matter. President Trump did not speak to the administrator directly, according to a third individual, but instead called Pruitt’s top deputy, former coal lobbyist Andrew Wheeler, to inform him that he would be taking the helm of the agency.

Soon after, Trump announced in a two-part tweet that he had accepted Pruitt’s resignation.

‘‘Within the Agency Scott has done an outstanding job, and I will always be thankful to him for this,’’ Trump wrote.

White House chief of staff John Kelly, who traveled with Trump to a political rally in Montana on Thursday, had for months privately groused about Pruitt’s conduct and had pushed for his removal during West Wing meetings, according to White House officials who were not authorized to speak publicly. But the timing of Thursday’s move took some White House officials by surprise, as the president had closely guarded the decision.

In a resignation letter released by the EPA, Pruitt wrote that it had been ‘‘a blessing’’ to serve under Trump and undertake ‘‘transformative work’’ at EPA. But he added that ‘‘the unrelenting attacks on me personally, my family, are unprecedented and have taken a sizable toll on all of us.’’

He signed the letter, ‘‘Your Faithful Friend, Scott Pruitt.’’

Trump later told reporters aboard Air Force One that there was ‘‘no final straw’’ that led to Pruitt’s departure, and that the move, which he said was of Pruitt’s volition, had been in the works for ‘‘a couple of days.’’

‘‘He came to me and said, ‘I have such great confidence in the administration. I don’t want to be a distraction,’ ‘‘ Trump said. ‘‘And I think Scott felt that he was a distraction.’’

Wheeler, a former Senate staffer and EPA employee who spent a decade representing coal, mining, and other energy companies, will become acting administrator on Monday, Trump tweeted.

Democrats and environmentalists hailed Pruitt’s exit, even as they viewed Wheeler’s rise warily and warned that he would continue many of the same policies. Senator Thomas Carper of Delaware, the top Democrat on the Senate Environment and Public Works Committee, said Thursday that Pruitt’s ‘‘brazen abuse of his position’’ had surprised even his political opponents.

‘‘We had a good idea what he was going to be on the policy side,’’ Carper told reporters. “We had no idea how morally bereft he would be. He was all the things this administration said it was opposed to. . . . He’s done a lot of damage. It can be reversed, but it’s going to take some time.’’

The chairman of the Environment and Public Works Committee, Wyoming Republican John Barrasso, said that Trump ‘‘made the right decision in accepting Pruitt’s resignation.

‘‘It has become increasingly challenging for the EPA to carry out its mission with the administrator under investigation.’’

During his roughly 16 months in office, Pruitt took steps to reverse more than a dozen major Obama-era regulations and overhauled key elements of the agency’s approach to scientific research. For months, he had ranked as a personal confidant and influential policy adviser to the president, commiserating with Trump over negative news coverage while praising the commander in chief for his intelligence and political acumen.

As scrutiny of Pruitt grew in recent months, Trump initially stood by his EPA chief. The president tweeted in early April that Pruitt was ‘‘doing a great job,’’ despite revelations about costly travel funded by taxpayers. Trump publicly defended Pruitt and praised his job performance as recently as early June.

Pruitt also endured contentious hearings recently on Capitol Hill during which he admitted little culpability as lawmakers in both parties grilled him about his ethics and spending decisions.

But the EPA leader continued to be dogged by bad publicity, as alleged spending excesses were described by current and former aides to congressional lawmakers.

The Washington Post reported that a lobbyist had helped arrange Pruitt’s $100,000 trip to Morocco last December, only to later receive a $40,000-a-month contract to promote that country’s interests.

Documents obtained under the Freedom of Information Act showed the same pattern for a visit the administrator wanted to make to Australia. That trip was canceled at the last minute, as was a trip to Israel, which had been lined up in part by casino magnate and Republican donor Sheldon Adelson.

Combative and unapologetic, Pruitt spoke with the rapid-fire delivery of a trial lawyer when outlining his policy positions or addressing audiences. While serving as Oklahoma’s attorney general, he made a name for himself in conservative circles by suing the EPA 14 times. And after taking over the EPA, he spent the bulk of his time meeting privately with industry leaders regulated by his agency, including top executives from the fossil fuel, agriculture, and chemical sectors.

In the early months of the Trump administration, when other Cabinet members were struggling to recruit deputies and navigate their departments, Pruitt was already unraveling federal restrictions on greenhouse-gas emissions and toxic-waste discharge from coal-fired power plants. He declined to ban a commonly used pesticide linked to potential neurological damage in fetuses, as the agency had previously proposed.

And he pushed Trump to announce a US withdrawal from the landmark Paris climate accord. He questioned not only the science of climate change but also the overwhelming scientific consensus that human activity is the primary contributor to global warming. He fundamentally altered the makeup of key scientific advisory boards, adding industry voices and barring scientists who had received EPA grants.

The moves made him a lightning rod for controversy.