He was the eldest son and heir of Henry de Bohun, 1st Earl of Hereford (1176–1220) by his wife Maud de Mandeville (alias Maud FitzGeoffrey), daughter and heiress of Geoffrey Fitz Peter, 1st Earl of Essex.

In 1258, after returning from a pilgrimage to the Holy Land, Humphrey fell away, like his father, from the royal cause to that of the barons.

The alliance of Simon de Montfort with Llywelyn ap Gruffudd of North Wales brought Bohun back to royal allegiance.

He headed the first secession of the Welsh Marchers from the party of the opposition (1263), and was among the captives whom the Montfortians took at the Battle of Lewes in 1264.

Humphrey was selected as one of the twelve arbitrators to draw up the Dictum of Kenilworth (1266), by which the disinherited rebels were allowed to make their peace.