His sole successful play was Junius Brutus in 1734, which ran for six nights at Theatre Royal, Drury Lane.
His competition was Farinelli singing at the Little Theatre, Haymarket, and Duncombe said that the "quivering Italian eunuch" was too much for the stiff Roman statesman.
Duncombe, however, had apparently intended a more traditional Whig play, along the lines of Addison's Cato, for he was aligned squarely against the "Tory" Scriblerians.
Alexander Pope satirized the London Journal by name in The Dunciad, and Duncombe had written a letter to it criticizing John Gay's The Beggar's Opera for its vitiating effects on public morals.
Between 1757 and 1759, he and his son, John Duncombe (who married the daughter of Joseph and Susanna Highmore), published The Works of Horace in English Verse.