John Russell was married on 28 August 1946 to Susan Doniphan Lindsay, daughter of the poet Vachel Lindsay. They had three daughters: Lady Felicity Anne Russell (born 2 September 1945), Lady Sarah Elizabeth Russell (born 16 January 1946), and Lady Lucy Catherine Russell (21 July 1948 – 11 April 1975). Neither Sarah or Lucy married or bore children; Felicity had one daughter, Rowan. Like their father and mother, the three daughters suffered from serious mental health challenges. Lucy, who was Bertrand Russell's favourite grandchild, died from self-immolation, at the age of 26, in the forecourt of a church near Penzance, ostensibly protesting in the cause of world peace.
John Russell had a distinguished early career, working for the FAO among other organisations, but in later life he was diagnosed as schizophrenic. Moreover, there was evidence that his father had an affair with his wife and this exacerbated his mental disorder and ensuing divorce. This made him the only person in the United Kingdom to be denied the vote on two counts, first, for being a peer and, second, for being insane. He made a speech in the House of Lords that was considered so outlandish that to this day it is the only speech unrecorded by Hansard.
John Russell was succeeded as Earl by his half-brother, the historian Conrad Russell, 5th Earl Russell.