He entered the navy in 1807, on board the sloop HMS Nautilus, under the command of Captain Matthew Smith, with whom he continued in HM frigates Comus and Nymphen, on the Lisbon, Mediterranean, North Sea, and Channel stations till August 1815.

During the last few weeks of the Nymphen's commission, Nias, in command of one of her boats, was employed in rowing guard round HMS Bellerophon in Plymouth Sound, keeping off the sightseers who thronged to catch a glimpse of Napoleon.

He continued in active service after the peace, and in January 1818 was appointed to the brig Alexander, with Lieutenant William Edward Parry, for an expedition to the Arctic under the command of Sir John Ross.

In 1826 Nias went out to the Mediterranean as first lieutenant of HMS Asia, carrying the flag of Sir Edward Codrington, and, after the battle of Navarino, was promoted to be commander on 11 November 1827, and appointed to the brig HMS Alacrity, in which he saw some sharp service against the Greek pirates who at that time infested the Archipelago, and especially on 11 January 1829, in cutting out one commanded by a noted ruffian named Georgios, who was sent to Malta and duly hanged.

[1] Nias was advanced to post rank on 8 July 1835, and in May 1838 commissioned HMS Herald, frigate, for the East Indies, a station which at that time included Australia, China, and the Western Pacific.

Though duelling was then not quite extinct, the feeling of the navy was strongly opposed to it, and Nias took the then unusual practice of bringing an action against Scott, who, after the evidence of Sir Thomas Herbert and others, withdrew the imputation, and under pressure from the lord chief justice expressed his regret, on which the plaintiff accepted a verdict of 40s.