Plummer’s origins are obscure, but by 1780 he was a merchant at 48 Lime Street, London. By 1793 he was a partner in the West Indian merchant firm of Plummer and Barham, then of 5 Billiter Square and subsequently of 2 Fen Court, Fenchurch Street, with Joseph Foster Barham. Much of their business correspondence survives and largely concerns shipments of rum.
By 1805 the firm of Plummer, Barham and Plummer had moved to 2 Philpot Lane, but they returned to Fenchurch Street in 1816.
