In April 1781 he entered the Royal Navy as a volunteer on board the frigate HMS Artois, with Captain John MacBride, and in her was present at the Battle on the Dogger Bank.

Early in 1798 Brilliant was sent out to join Admiral Waldegrave on the Newfoundland Station; and on 26 July, whilst standing close into the bay of Santa Cruz in quest of a French privateer, she observed the frigates Vertu and Régénérée preparing to sail for Rochefort.

[5] Early in 1799, Brilliant returned to England, and Blackwood was appointed to the frigate HMS Penelope, of 36 guns, in which, after a few months of Channel service, he was sent out to the Mediterranean, and employed during the winter and following spring in the close blockade of Malta.

During the next two years he was employed on the coast of Ireland or in the Channel, and in July 1805 was sent to watch the movements of the allied fleet under Villeneuve after its defeat by Sir Robert Calder.

[1] On his return with the news that Villeneuve had gone to Cadiz, he stopped on his way to London to see Nelson, who went with him to the Admiralty, and received his final instructions to resume the command of the fleet without delay.

He was offered a line-of-battle ship, but preferred to remain in Euryalus, believing that he would have more opportunity of distinction; for Villeneuve, he was convinced, would not venture out in the presence of Nelson.

He was thus in England at the time of Lord Nelson's funeral (8 January 1806), on which occasion he acted as train-bearer of the chief mourner, Sir Peter Parker, the aged admiral of the fleet.

On 4 June 1814, Blackwood attained the rank of rear-admiral[1] of the Blue and in September he was created a Baronet,[7] for his conduct of the heads of royal families of Europe to England following the defeat of Napoleon.

In August 1819 he was made a Knight Companion of the Order of the Bath, and appointed commander-in-chief of the East Indies Station, nearly suffering a shipwreck in Leander on his way there off the coast of Madeira.

[9] He died after a short illness, differently stated as typhus or scarlet fever, on 17 December 1832, at Ballyleidy, the seat of his eldest brother, Lord Dufferin and Claneboye.