Grant married voice coach Joan Washington in 1986 and has one daughter with her, Olivia, and a stepson, Tom.
Grant is a teetotaller.
His body has an intolerance of alcohol, having no enzymes in the blood to metabolise it.
If he does drink alcohol, he can keep it down for 10 minutes and is then violently sick for 24 hours afterward.
After casting him as the alcoholic Withnail, director Bruce Robinson made Grant drink a bottle of champagne and half a bottle of vodka during the course of a night so that he had experienced the sensation of being drunk.
At age 12 he "developed a rhapsodic crush" on Barbra Streisand and remains a fan.
 He has done a tour of Streisand's New York, visiting her early home, her high school, and the Village Vanguard, among other places.

Grant is a dual citizen of the United Kingdom and Eswatini (formerly Swaziland).
He used to wear a watch on each wrist, one given to him by his dying father, permanently set on Swaziland time.

In October 2008, Grant told The Times that he is an atheist.
He is an avid supporter of Premier League football club West Ham United.
In April 2014, Grant launched his new unisex perfume, JACK, exclusively at Liberty of Regent Street, London.
Grant runs the perfume business in collaboration with his daughter.
Grant married voice coach Joan Washington in 1986 and has one daughter with her, Olivia, and a stepson, Tom. Grant is a teetotaller. His body has an intolerance of alcohol, having no enzymes in the blood to metabolise it. If he does drink alcohol, he can keep it down for 10 minutes and is then violently sick for 24 hours afterward. After casting him as the alcoholic Withnail, director Bruce Robinson made Grant drink a bottle of champagne and half a bottle of vodka during the course of a night so that he had experienced the sensation of being drunk. At age 12 he "developed a rhapsodic crush" on Barbra Streisand and remains a fan.  He has done a tour of Streisand's New York, visiting her early home, her high school, and the Village Vanguard, among other places.
Grant is a dual citizen of the United Kingdom and Eswatini (formerly Swaziland). He used to wear a watch on each wrist, one given to him by his dying father, permanently set on Swaziland time. 
In October 2008, Grant told The Times that he is an atheist. He is an avid supporter of Premier League football club West Ham United. In April 2014, Grant launched his new unisex perfume, JACK, exclusively at Liberty of Regent Street, London. Grant runs the perfume business in collaboration with his daughter.
Richard E. Grant