In 1733 Smythe, a practising lawyer, was recommended to Sir Philip Yorke by the Duke of Dorset as
a very sensible young fellow and I hope will deserve any favour you are pleased to show him; he is related to the Duke of Newcastle and my Lord Leicester; he is not easily distinguished by his surname which is a very common one, but his christian name is not so.
22 Sept. 1733, Add. 35585, f. 193.
He was brought in by the Duke as a Whig for East Grinstead in 1747, vacating his seat in 1750 on being made a baron of the Exchequer. In April 1754 he declined promotion in another court writing: ‘I am so well pleased with the court in which I am placed, that I have at present no desire of removing from it.’ He again declined promotion on the death of the lord chief baron in 1755.
He died 2 Nov. 1778.