John Tuchet, 8th and last Earl of Castlehaven; 18th Baron Audley; 6th and last Baron Audley of Hely (2 August 1724 - 22 April 1777) was the son of James Tuchet, 6th Earl of Castlehaven and his wife née Elizabeth Arundell. He succeeded his brother as Earl of Castlehaven, Baron Audley, and Baron Audley of Hely on 6 May 1769.
He died unmarried, at which time the Earldom of Castlehaven and the Barony of Audley of Hely became extinct. The Barony of Audley created by writ of 1312 is deemed to have devolved upon his nephew, son of his sister Elizabeth, namely George Thicknesse, later Thicknesse-Touchet.
{| border="2" align="center"
|-
|width="30%" align="center" rowspan="2"|Preceded by:
James Tuchet
|width="40%" align="center"|Earl of Castlehaven
|width="30%" align="center"|Followed by:
Extinct
|-
|width="40%" align="center"|Baron Audley
|width="30%" align="center"|Followed by:
George Thicknesse-Touchet
|}
