In 1733 he inherited the greater part of his father's personal property at the expense of his half-brother, Corbet Kynaston, whom he succeeded at Bryngwyn and Hardwick in 1740.
[3] At the 1734 British general election Kynaston was returned as a Tory Member of Parliament for Bishops Castle on the interest of John Walcot.
He acted as teller on the Government side in the division on Dowdeswell's motion on the cider bill on 31 January 1764.
On 9 May 1765 during the crisis over the Regency bill, he seconded Morton's motion to include the Princess Dowager among those capable of being appointed Regents, although he said nothing at all in support of it.
He left Grenville and voted with Administration over John Wilkes and the Middlesex election on 3 February and 8 May 1769.