Member of a junior branch of the Bertie family seated at his mother's estate of Low Leyton, Essex, he was returned for Westbury from 1753 to 1774 by the senior branch of the family, the Earls of Abingdon, where he was in continuous opposition to the successive Whig administrations.
[2] Their son, Peregrine Bertie, entered the Middle Temple on 29 February 1739/40,[3] and matriculated at Magdalen College, Oxford on 12 December 1740 at the age of 17.
[3] On 18 October 1753 at All Saints, Little Billing, Northamptonshire, by licence, he married Catherine (died 2 July 1770), the daughter of Richard Backwell.
[6] Bertie's fourth cousin, the 3rd Earl of Abingdon, a Tory, had a strong electoral interest in Westbury.
The death of one of these, Matthew Michell, in 1753, allowed Abingdon to return Bertie for Westbury in the Tory interest.