James Vashon entered the Royal Navy at age thirteen, in 1755, and first served aboard the 28-gun frigate HMS Revenge under Captain Cornwall.

As a midshipman he served on a number of vessels and saw combat service in the Mediterranean, the coast of North America, and in the Caribbean.

He achieved recognition with his action during the capture of the French ship Lion, when he was given command of the prize and over 200 prisoners, and successfully reached the British naval base at Antigua.

In late 1786 Vashon was recalled to service and took command of the 50-gun HMS Europa, where serving under him were Midshipmen James Baker and Peter Puget, and Lieutenant George Vancouver, who would become significant in future explorations of the area of Washington state.

In April 1804 Vashon was promoted to Rear-Admiral in command of the Leith Station, Scotland with his flag aboard HMS Roebuck.

He instituted a formal convoy system out of Leith to protect this vital shipping route, and was so successful that he was promoted to Vice-Admiral in 1808.

When Vashon decided to retire in late 1808, the merchants and leaders of Leith were so pleased that they gave him a public dinner, awarded him two commemorative plates, and honoured him as a Freeman of the City of Edinburgh.