He was educated at City of Norwich School and won a scholarship to study English at Downing College, Cambridge for a year in 1941, where he was a pupil of F. R. Leavis.
Holbrook was called up for military service with the British Army in 1942 and served until 1945 as an officer with the East Riding Yeomanry.
His first novel, Flesh Wounds (1966), told the story of the escapades of Paul Grimmer (Holbrook's fictionalised persona) as a tank officer in the Normandy invasions.
The events of Grimmer's adolescent life up to his enlistment were recounted in A Play of Passion (1978), which told of his involvement with the Maddermarket Theatre and its founder Nugent Monck.
His grandfather William built wagons in the Midland and Great Northern Railway workshops at Melton Constable.
His other novels are Nothing Larger Than Life (1987); Worlds Apart (1988); A Little Athens (1990); Jennifer (1992); The Gold in Father's Heart (1992); Even If They Fail (1994); and Getting It Wrong With Uncle Tom (1998).