Greater Manchester Police was directly created from two recently amalgamated city police forces, Manchester and Salford Police and parts of what were Lancashire Constabulary, Cheshire Constabulary and West Yorkshire Constabulary on 1st April 1974. The city forces were Manchester Borough Police which formed in the late 1830s and Salford Borough Policewhich began in 1844. Upon Manchester gaining city status in 1853, its police force changed its name to Manchester City Police to reflect its status. In 1926, Salford also became a city, resulting in Salford Borough Police becoming Salford City Police. These two city forces operated until 1968 when, as a result of compulsory amalgamation, as per the Police Act 1964, Salford City Police merged with Manchester City Police, resulting in the new force of Manchester and Salford Police. This new force lasted only 6 years, when in 1974 the Local Government Act 1972 created the Metropolitan County of Greater Manchester and with it, Greater Manchester Police. An increase of 284,241 acres in terms of policing area and 2,267,090 people over the abolished Manchester and Salford Police.

Indirectly GMP can also trace its heritage to a number of other borough forces, each with their own significant history, which had been abolished in the late 1960s (under the Police Act 1964) and which had been amalgamated into the county forces of Lancashire and Cheshire. These two county forces only policed these boroughs for around 6 years before Greater Manchester was created and GMP took over responsibility for providing police services. In the historic Lancashire county area these borough police forces were Bolton Borough Police (1839-1969) , Oldham Borough Police (1849-1969), Rochdale Borough Police (1857-1969) and Wigan Borough Police (1836-1969). In the historic Cheshire county area this included Stockport Borough Police (at least 1835-1967).

The first Chief Constable of GMP was William James Richards. Richards had been the chief constable of the short lived Manchester and Salford Police (1968 to 1974) and before that chief constable of Manchester City Police (1966 to 1968). Following his retirement on 30 June 1976, James Anderton became the new chief constable on 1 July 1976.  James Anderton was a controversial figure during his 15 years in office due to his outspoken style of leadership and hardline views on crime, policing and morality. In 1991 David Wilmot succeeded James Anderton. In 2002 Michael Todd was appointed to Chief Constable until his death, by suicide, in 2008.