Jemma and her husband Tim have two sons, Gabriel (born 1994) and Alfie (born 2000).
She is married to Tim Owen Q.C., a London lawyer. He has written several legal text books, including Prison Law and Asset Recovery, and is an advisory editor of Blackstone's Criminal Practice.
Jemma is a graduate of LAMDA - the London Academy of Music and Dramatic Art.
Jemma is the daughter of Corin Redgrave, the niece of Vanessa and Lynn Redgrave, the cousin of Natasha and Joely Richardson, the grand-daughter of Sir Michael Redgrave and Rachel Kempson, and the great-grand-daughter of Roy Redgrave - all of them actors.