The first detective branch of the DMP was formed of 12 constables under the command of Inspector James O'Connor (No. 688, B Division), on the 27th October 1842. The immediate success of this special branch resulted in the Commissioners of the DMP establishing a dedicated division - G Division - on the 17th March 1843.
G Division was based at the Detective Office, Exchange Court (Dublin Castle), until January 1916, when it moved to the new building in Great Brunswick Street. It was permanently staffed and able to respond to crime reports at all hours.