In 1732, but a fifteen year old, Colvill left his home at Dundee, in order to join the British navy. Though coming from an aristocratic family in Scotland, Colvill had no particular connections in the navy and his advancement during his first number of years was slow.
By 1744, however, we see (DCB) where Colvill was the captain the 20 gun, Leopard. In was in this ship that he distinguished himself, mainly, as being very efficient in capturing privateers. It would appear Colvill concerned himself not too much with the flag it flew, or the papers carried, the valuable cargoes of these smaller vessels captured eventually ended up as credits in his accounts back in England.
In 1753, Colvill was given command of one of the British navy's largest vessels, the 70 gun, Northumberland, a ship that was under his command for most of The Seven Years War.
Beginning in 1755, Colvill in his Northumberland was to be in the waters off of Louisbourg with Boscawen. (See "Action at Sea, Off of Louisbourg.") In 1757, he returned to Nova Scotia to be with Holburne's fleet which was caught in a bad autumn storm off the coast of Cape Breton. (See "The Storm.") As one might see from my accounting of events, Colvill, who brought the storm bashed Northumberland in to Halifax, was ordered by Holburne to winter over at Halifax as the officer in charge; and, to sweeten the deal, Holburne made Colvill a commodore, right on the spot.
During the winter of 1757/1758, Colvill made the eight men-of-war which had wintered over ready for sea, notwithstanding, that, he had to contend with: storm damaged ships; severe winter weather; lack of facilities and naval supplies. Much to Colvill's credit he had the fleet ready by April, 1758; and it joined Hardy's fleet which arrived off the coast directly from England; the whole to run a blockade off of the mouth of Louisbourg. Thus, it was, that Colvill participated in the successful Siege of Louisbourg.
In the 1759 campaign, Colvill was with Durell's fleet of large ship which patrolled the lower reaches of the St. Lawrence.
During the latter years of the war, though sick ("sore throats, swelled legs, innumerable pains all over me, sciatica, scurvy, rheumatism"), Colvill devoted himself to the building of the dockyard facilities at Halifax. In 1762, he was recalled to England, and, at that time, promoted to rear-admiral. In 1763, though reluctantly, Colvill accepted a new promotion of a new North American command. He was to station himself at Halifax. "the best place in the whole extent of America for refitting the King's ships." An observation was also made, that there were fewer opportunities at Halifax for desertion as there were at more southerly ports.
Being replaced by Durell, in 1766, Rear-Admiral Alexander Colvill retired to England.
Though briefly married, Colvill left no legitimate heirs, though he had children by at least three different women; all of whom, "his family," he left instructions and funds behind for their continuing care.