The director of the Secret Service, Kimberly A. Cheatle, resigned on Tuesday, after security failures surrounding the attempted assassination of former President Donald J. Trump and calls for her to step down from prominent Republican lawmakers.

In an email to Secret Service employees on Tuesday, Ms. Cheatle said that one of the Secret Service’s foremost duties is to protect the nation’s leaders and that the agency “fell short of that mission” in failing to secure a campaign rally from a gunman on July 13.

“I do not want my calls for resignation to be a distraction from the great work each and every one of you do towards our vital mission,” Ms. Cheatle said in the email, which was reviewed by The New York Times.

She said she was deeply committed to the agency but added that, “in light of recent events, it is with a heavy heart that I have made the difficult decision to step down as your director.”

President Biden, in a statement Tuesday, thanked Ms. Cheatle for answering his call to lead the agency. “As a leader, it takes honor, courage and incredible integrity to take full responsibility for an organization tasked with one of the most challenging jobs in public service.”

Mr. Biden said he would appoint a new director soon.

The resignation is a rapid fall for the agency veteran who protected Dick Cheney and Mr. Biden in their vice-presidential tenures and was publicly supported by Biden administration officials after the gunman shot at Mr. Trump. The glaring security mistakes before the shooting, however, and the heated criticism that Ms. Cheatle faced in the days since had left her position increasingly in doubt.

Mr. Biden gave high praise to Ms. Cheatle in an announcement of her appointment to the position in August 2022. Mr. Biden said in a statement then that his family “came to trust her judgment and counsel” and that she had the president’s “complete trust.” She worked for the agency for nearly three decades.

But her fortunes changed when Mr. Trump was injured in the shooting at a campaign rally in Butler, Pa., on Saturday, July 13, though he was pulled off the stage and pronounced safe. A former local fire chief attending the rally, Corey Comperatore, was killed. Two other attendees were hospitalized.

Compounding matters, on Monday, Ms. Cheatle faced a contentious group of lawmakers at the House Oversight Committee who were frustrated at her lack of specific answers on what happened that led to the assassination attempt on Mr. Trump. At one point, Representative Marjorie Taylor Greene, Republican of Georgia, asked for a timeline from the day of the shooting.

“I have a timeline that does not have specifics,” she said.

By the end of the hearing, lawmakers from both parties were calling for her to step down, including Representative Jamie Raskin of Maryland, the top Democrat on the committee.

“The director has lost the confidence of Congress, at a very urgent and tender moment in the history of the country,” Mr. Raskin said.

Homeland Security Secretary Alejandro N. Mayorkas, to whom the Secret Service answers, previously described the shooting as a security failure.

Almost immediately after the shooting, Ms. Cheatle faced an onslaught of criticism from Republican lawmakers who said she was directly to blame for security lapses surrounding the attempt on Mr. Trump’s life.

She described the agency’s performance as “unacceptable,” in interviews after the shooting.

“The buck stops with me,” she said in an interview with ABC News on July 15. “I am the director of the Secret Service, and I need to make sure that we are performing a review and that we are giving resources to our personnel as necessary.”

Last week, Senators John Barrasso of Wyoming and Marsha Blackburn of Tennessee, both Republicans, tracked Ms. Cheatle down at the Republican National Convention. Ms. Cheatle led security for the event, where Mr. Trump accepted the nomination.

“You put him within less than an inch of his life,” Mr. Barrasso said in a video capturing the interaction. “So resignation or full explanation.”

In the days after the shooting, top Biden administration officials publicly backed Ms. Cheatle, including Mr. Mayorkas.

“I will tell you that my confidence in Kim is 100 percent,” he said three days after the shooting.

Ms. Cheatle served in several leadership roles at the agency, including as an assistant director, during her tenure. In 2019, she took a position as a lead security official for PepsiCo in North America, before returning to the agency in September 2022