On April 1, 1963, a resolution creating the Gaithersburg Police Department was signed by Mayor Merton F. Duvall. This resolution specified a traffic unit to be created within the Department; however, such a unit was not formed until 1983.

Chief David Marstiller was the first Chief of Police, although there are references to a “Town Marshall” in the minutes of Town Council Meetings prior to 1963. The town budget for FY64 included “police protection” salaries for the solitary officer amounting to $4,000, and equipment purchases of $500.

Over the years, the department has been led by a number of distinguished Chiefs of Police. The first was James Tassie, who came to the position from the Rockville City Police Department. He was followed by Marson Johnson, previously an officer in Michigan. Leadership later passed to John F. DeVries and George Fusco, both of whom retired from the Montgomery County Police Department at the rank of Lieutenant. In 1986, Mary Ann Viverette became Chief and served until her retirement in May 2007. She was succeeded by John King, who had retired from the Montgomery County Police Department as an Assistant Chief and led the agency until 2010. Mark P. Sroka, a retired Major from the Maryland State Police, then served as Chief until his retirement in 2026. Today, the department is under the leadership of Chief Shawn Eastman.

The Department grew from an authorized strength of three sworn officers and one civilian clerk in the early 1970s, when the City's population was approximately 7,000. Today, with a population exceeding 73,000, the Department’s complement has expanded to 70 sworn officers and 23 non-sworn personnel.

It was under the administration of Chief DeVries that the City Police began to operate under its current system of dispatch through the Montgomery County Police. As a retired Montgomery County Police Lieutenant, DeVries was in a position to work with the County Police in a way that had previously not been possible.

While the Department sent an untrained officer to a police academy in 1971, that was not to occur again until 1990. During the interim 19 years, only experienced officers from other agencies were considered for employment with the Department.

The majority of the Gaithersburg Police Officers have come from other agencies. The experience of these officers comes from agencies such as Montgomery County, Washington, D.C., United States Secret Service, Montgomery County Sheriff’s Office, Maryland National Capital Police, and Baltimore City, to name a few. This diversity in officer experience has resulted in an agency made up of highly-trained individuals with a variety of special abilities.