Educated first in Paris, he was admitted to Trinity Hall, Cambridge in 1802, and inherited his father's Berechurch estate in 1805—which he extended and rebuilt, making him popular and respected in the local Colchester area—and the Baronetcy of Upton.
In particular, he was a "diehard opponent" Catholic emancipation, "dividing doggedly against it" and presenting a petition to the House of Commons to "guard the country from the danger to which it was exposed from the machinations of men who were avowedly hostile to the church establishment" if the Test Acts were repealed.
Ultimately, however, he resigned his parliamentary seat in 1829 "in disgust" at the Wellington–Peel ministry's concession of Catholic emancipation, by accepting the office of Steward of the Chiltern Hundreds.
[4] Smyth returned to the seat at the 1835 general election, then holding it until 1850 when he again resigned, due to "age and infirmities", accepting the office of Steward of the Chiltern Hundreds.
[3][4][6] Smyth died at his home in Berechurch in 1852, leaving no legitimate issue, with his estate being passed to the children of his illegitimate daughter, Charlotte, who had married Thomas White of Wetherfield, Essex.