Debrett was of French Huguenot background and took over the business of John Almon, opposite Burlington House in Piccadilly, in 1781.
His shop continued to be the resort of the whigs, the Pittites going chiefly to his neighbour, Stockdale.
He died at his lodgings in Upper Gloucester Street, Regent's Park, on 15 November 1822.
Among Debrett's publications were a new edition of The New Foundling Hospital for Wit (1784), 6 vols., and Asylum for Fugitive Pieces in Prose and Verse (1785–1788), 4 vols.
The first edition of The Baronetage of England, containing their Descent and Present State, by John Debrett, 2 vols., appeared in 1808.