During 1801 and 1802 he served as surgeon of different small craft in the Channel, and being left by the peace without employment, half-pay, or any chance of a practice on shore, he accepted an appointment as surgeon of the ship Trusty, Davidson, master, bound from London to the coast of West Africa, in the slave trade, which sailed in January 1803.

At Whydah, which he describes as being then esteemed "the Circassia of Africa", on account of the comeliness and jetty blackness of its maidens, he was left in charge of a factory for purchasing slaves, while the Trusty went on to Lagos.

Thereupon, Davidson, assisted by the masters of three or four other English ships at that port, attacked and captured a large French slaver, named the Julie, which had been spoiling their market.

Here, with his leave being expired, Sir John Buckworth the commander-in-chief, appointed him to the Flying Fish, a small cruiser under the command of an energetic young lieutenant, "and for the next year", he says, "we roamed through each creek and corner of the Caribbean sea, and plundered every enemy of England without the risk of incurring the penalties of piracy".

In July 1818 he was appointed surgeon of the Royal Sovereign yacht, and in the following year, encouraged by the success of his literary venture, he put together a short and pleasantly written account of his experiences as a slaver, which was published under the title of A Voyage to Africa, with some Account of the Manners and Customs of the Dahomian People (1820, 12mo).