D.C. Police Chief Cathy Lanier announced she will retire from the department after 26 years of service. But her work with law enforcement is not over; she is joining the NFL.

Lanier's last day will be Sept. 17, Mayor Muriel Bowser said during a news conference Tuesday afternoon. Bowser said she will name an interim police chief in the coming days.

Lanier accepted a position as senior vice president of security for the NFL. She will begin work at the league's New York office next month, NFL Commissioner Roger Goodell announced Tuesday.

"It is an honor for me to move to the next stage of my career knowing that I can use the experience and education that I have gained over the past 26 years to protect and serve all of the NFL, its fans, players and employees,'' Lanier said in a letter to the department's 3,700 officers.

In her new job, Lanier will oversee the security of all 32 NFL teams and their venues, working with federal, state and local law enforcement and handling security for the Super Bowl.

"Cathy joins us with a well-deserved reputation of being a tremendous communicator, innovator and relationship builder,'' Goodell said.

Lanier, a Maryland native who dropped out of high school in 9th grade and became a mother at age 15, came from a family of police officers and joined the department in 1990 after earning a high-school equivalency diploma.

Chief @DCPoliceDept to take VP security job @NFL according to sources — Mark Segraves (@SegravesNBC4) August 16, 2016

In 2006, she was tapped to be the commanding officer of the department's Office of Homeland Security and Counter-Terrorism (OHSCT). A year later, she was named chief of police, becoming the second woman to hold the position.

Sonya Proctor served as interim chief of police from November 1997 to April 1998.

"Your attitude and your effort will get you where you want to go," Lanier said when asked what advice she would give to a young person.

The number of violent crimes reported in the District had already decreased significantly by the time Lanier became chief. Homicides continued to drop to a low of 88 in 2012, but by 2015, slayings increased by more than 50 percent. Killings this year are continuing at 2015's pace.

Her retirement leaves Bowser with two important positions to fill. D.C. Public Schools Chancellor Kaya Henderson will step down this fall, Bowser announced in June. Her last day is Sept. 30.

RAW VIDEO: Police Chief Cathy Lanier announces her plans to retire from D.C.’s Metropolitan Police Department. She will join the NFL as senior vice president of security.

Battles With Police Union

During her tenure as police chief, Lanier has had many public battles with the Fraternal Order of Police.

Last year, more than 1,000 police officers in D.C. said they had "no confidence" in her ability to manage the Metropolitan Police Department and keep the public safe.

The union said the "no-confidence" vote was a symbolic gesture.

D.C. Police Chief Cathy Lanier’s retirement leaves Mayor Muriel Bowser with two important positions to fill, as Schools Chancellor Kaya Henderson previously announced she will step down in September. News4’s Tom Sherwood reports.

Both Lanier and Bowser dismissed the survey, noting fewer than a third of the of the officers participated.

The vote follwed 2015's spike in violent crimes and an an "All Hands On Deck" initiative instituted by Lanier. The initiative, which Lanier started in 2007, aimed to limit spikes in crime by flooding the streets of D.C. with officers.

On Tuesday, Matt Mahl, the chairman of the Fraternal Order of Police, thanked Lanier for her service and cooperation.

Cathy Lanier’s time as D.C.’s police chief spanned a period of great change in the city and in policing in general. News4’s Jackie Bensen reports.

"Her cooperation has been felt by our membership at large," Mahl said. "We are curious to meet her replacement and we look forward to continuing our current relationship with the next chief."

But Greg Pemberton, the treasurer of the Fraternal Order of Police, had a different opinion of Lanier's departure, calling it the "greatest day in his career" on Twitter.

"Lanier should be ashamed that she's leaving the department in such disarray. 994 officers have fled in just two and a half years, and morale has never been worse," Pemberton said.

The Associated Press contributed to this report.