Piercy was commissioned lieutenant on 14 February 1757 and promoted commander on 18 April 1778.
Commanding the hired ship Countess of Scarborough 20, he was present when the Medea 28, Captain James Montagu, captured the Dunkirk-based cutter privateer Duc de Lavaugnon 14 on 16 June 1779, and he was then despatched by Montagu to find and capture her consort, the Comte de Maurepas 14.
At the Battle of Flamborough Head on 23 September 1779 the Countess of Scarborough surrendered to the Pallas 32 after a two hour defence, having suffered casualties of four men killed and twenty wounded, and with seven guns out of action and her rigging in tatters. In the same engagement the Serapis 44, Captain Richard Pearson, surrendered to the Bonhomme Richard, commanded by John Paul Jones. Piercy was acquitted of his vessel’s loss at his eventual court-martial on 10 March 1780, and as well as receiving high praise for his defence he was rewarded by the Royal Exchange Assurance Company and given the freedom of Scarborough.
He was posted captain on 19 April 1780 and had the Squirrel 20 from the following month to 30 August 1781. Early in the following year he commissioned the Panther 60 at Portsmouth for the Channel Fleet campaign from April-August, but being in poor health he left her when she reached the Downs in May to be replaced by Captain Robert Simonton.
Piercy died on 22 September 1793 and was interred at Canterbury Cathedral.
His address in his will was given as Canterbury, Kent. He left a widow.
Piercy was very well liked by his officers and men and was regarded as an excellent officer.