She has both Bachelor of Science and Master of Science degrees in management from Johns Hopkins University and holds a Master of Arts in national security studies from the Naval Postgraduate School in Monterey, California. Her thesis was Preventing Terror Attacks in the Homeland: A New Mission for State and Local Police. She attended an executive education program at Harvard Kennedy School.
Lanier was appointed by Washington, District of Columbia Mayor Adrian Fenty in January 2007, replacing outgoing Police Chief Charles H. Ramsey. In May 2012, Mayor Vincent C. Gray agreed to retain Lanier as police chief under a new five-year contract. Lanier was raised in suburban Tuxedo, Maryland, on the northeast edge of the District of Columbia in Prince George"s County, Maryland.
She also performed part of her undergraduate studies at Prince George"s Community College, and the University of the District of Columbia - where she also received her General Educational Development. Lanier dropped out of junior high school after the ninth grade, and became a mother at the age of 15.
She now resides in the Fort Lincoln area of northeast Washington"s Ward 5, close to her hometown. Lanier joined the Metropolitan Police Department of the District of Columbia in 1990 as a foot patrolman.
In 1994 she was promoted to Sergeant, and, two years later, a Lieutenant, before becoming a patrol supervisor. In 1999, she became a Captain and, later that year, was promoted to Inspector and placed in charge of the Department"s Major Narcotics Branch/Gang Crime Unit.
In August 2000, she was promoted to Commander-in-Charge of the Fourth District of the city.
In April 2006, she became the Commander at the Office of Homeland Security and Counter-terrorism, Office of the Chief of Police in MPDC, overseeing, among other things, the bomb squad and the emergency response team Lanier came under fire in July 2009 after claiming that motorists who used Global Positioning System navigation and smartphones to avoid traffic cameras were employing a "cowardly tactic". The tactic has led to the arrest of out of town visitors who had extra tickets to see the Washington Nationals.
She publicly criticized a plainclothes officer, Detective Michael Baylor, who drew his gun on a group of civilians during a Washington, District of Columbia, Twitter-organized snowball fight as a response to snowballs hitting his vehicle on 19 December 2009.
Video footage and eye-witness accounts have been used in the investigation. Baylor was placed on desk duty during the investigation but returned to active duty following the completion of the investigation.
Lanier has defended the practice of arresting individuals reselling tickets to sporting events, even if the tickets were sold at face value.
