Police Constable James Gordon was attacked with iron bars as he stopped a gang of men breaking into a boiler works factory in St Helens, Merseyside, in 1893.
Although his death is listed in police records, his grave at St Helens Cemetery was left unmarked. But 120 years later Brenda Neary, a former Merseyside police officer and volunteer at the cemetery, has been able to track down his resting place.
The Police Roll of Honour Trust has commissioned the headstone to be erected on the grave at a ceremony to mark the anniversary of PC Gordon's death on November 13.
Steve Lloyd, manager of the trust, said: "We may never know why this local police hero was left in an unmarked grave in this cemetery for 120 years."