He was born at Mayfield, Sussex, eldest son of Thomas Jenner of that place, and Dorothy, his wife, daughter of Jeffrey Glyde of Dallington.
With the majority of the judges, Jenner gave judgment in favour of the king's claim to the dispensing power which was raised in the case of Sir Edward Hales.
Cartwright sought to have him dismissed from the commission, finding him too moderate if outwardly overbearing to the fellows, and in the end Jenner voted against the expulsions.
The king's general pardon to him and money were stolen at this point from his chambers in Serjeants' Inn; and he was captured at Faversham and brought to Canterbury.
They were admitted to bail, but the Convention parliament voted that Jenner was principally concerned in the arbitrary proceedings under James, and he was committed to the custody of the sergeant-at-arms.