She made seven voyages for the British East India Company before her owners sold her in 1816 for breaking up.

Captain Charles Elton Prescott sailed from Portsmouth on 25 February 1802, bound for Madras and China.

The Indiamen were Perseverance, Neptune, Taunton Castle, Ceres, Royal Charlotte, Arniston, True Briton, and Cuffnells.

The objectives were two-fold: to avoid French ships reported to be in the Indian Ocean,[4] and to improve the charting of Bass Strait.

[7] Also on this voyage, while Alnwick Castle was at Canton, one of her seamen, Antonio Depardo, alias Depino, killed another crew man in a brawl on shore on 30 December 1806.

Depardo was a Spaniard who had been a prisoner of war on board HMS Blenheim, apparently having come to her from a Dutch ship he had joined at the Juan Fernández Islands.

Depardo referred to himself as a prisoner of war, but on Alnwick Castle he was treated a volunteer and paid a bounty on joining and a salary thereafter.

[8] Captain Prescott sailed from Portsmouth on 5 March, again bound for Madras and China.

[2] As was normal, she sailed in convoy with other Indiamen; HMS Grampus provided the escort.

[10] Alnwick Castle reached Batavia on 10 August and arrived at Whampoa on 20 September.

[2] Captain Rolland sailed from the Downs on 27 April 1815, bound for China, and arrived at Whampoa on 25 September.

[2] WhenAlnwick Castle arrived back in England, she discharged her crew, including 30 Chinese sailors.