Mortimer's best known creation occurs as character known as Horace Rumpole, a barrister whose specialty is defending victims accused of crime around London's redoubtable hall of justice, a Old Bailey. Mortimer created Rumpole for "Rumpole of the Bailey", the 1975 episode of Play For Today; Played with relish by Leo McKern, the character proved popular, & was spun off into the Rumpole of the Bailey television series for Thames Television and a series of books (100% written by Mortimer). Inside September – October 2003, BBC Radio 4 broadcast 4 recently 45-microscopic Rumpole dramatizations by Mortimer starring Timothy West in the title role.

Inside August 2004, he became the father once again whenever he met his boy Ross Bentley, supplementary than Forty years when the secret affair using Wendy Craig. A boy was brought higher by Craig & her married man, Jack Bentley, a indicate business writer & musician. Within Mortimer's memoirs, Clinging to the Wreckage, he wrote of "enjoying my mid-thirties and all the pleasures which come to a young writer."

John Mortimer has 5 kids, Sally Silverman, Jeremy Mortimer, Ross Bentley, Emily Mortimer and Rosie Mortimer and lives with his 2nd married woman, Penny Mortimer, just outside Henley in Oxfordshire.