Marshall, born in Ramsgate, Kent, England, became an apprentice sailor at age ten, and spent his life at sea.

In 1788 he captained Scarborough, a ship of the First Fleet taking convicts from England to Botany Bay[1] in New South Wales.

John Marshall also captained Scarborough on her second voyage transporting convicts to Australia in 1790.

The convicts coming aboard were in poor health and many did not survive the voyage; this, combined with an attempted seizure of the ship by the convicts, deterred him from any further voyages of transportation.

During the Napoleonic Wars of 1803 to 1815, as captain of the ship Diana, he was severely wounded while repulsing an attack by a French privateer.