Llewellyn was born in Wiltshire, England, and studied medicine at Charing-Cross Hospital, graduating in 1859. He accepted employment on the CSS Alabama. During the battle with the USS Kearsarge he insisted that all wounded be removed from the sinking Alabama before he left. He stayed on board too long and was drowned as the ship sunk. His obituary stated that he was drown on June 19, 1864, off Cherbourg, France.