Nineteen Royal Marines and one Royal Navy Medic from 1 Troop, J Company, rowed 3,200km (1,988 miles) on rowing machines, completing the task in 56 hours and 47 minutes.
Raising money for the Royal Marines Charity, each man taking part rowed an average of 145km (90 miles).
A tweet from RFA Fort Victoria's official Twitter account said the group had finished the challenge.
"19 @RoyalMarines and 1 @RoyalNavy Medic from 1 Troop, J Company, completed their challenge to row the coast of the UK, 3,200km in 56 hours and 47 minutes.
"On average each man rowed 145km."
Cover image: Marines on the charity rowing challenge (Picture: RFA Fort Victoria Twitter).