Born in County Donegal in 1747, Conyngham arrived in America as a young man where he was apprenticed to a Captain in the West Indian Trade. He would later become a powerful player in the naval battles of the American Revolution. Yet his contemporaries regarded his exploits at sea with distaste, and he is often referred to as being more of a pirate than an honourable naval captain.
Whilst captaining a small merchant ship off the coast of Dunkirk, Conyngham and his men refurbished the ship as a war vessel and began a campaign of attacking and capturing ships, eventually taking charge of a British ship which they renamed Revenge. This act was detested by the British for Conyngham's blatant disregard of the neutrality of the French. The animosity would only worsen with time. Now equipped with a larger ship, the plundering continued, with several ships being captured on a journey around the British Isles and down the coast to Spain. Upon arrival in America the Revenge was sold at auction and Conyngham was placed in charge of a ship in the private sector. This was in punishment of his actions in Dunkirk, as he had violated the terms of his original commission by capturing British ships. Since he could not produce the commission, Conyngham had no way to clear his name of the corruption which he adamantly denied until his death.
It was while in command of the private ship that he was captured by the British and placed under guard at the Mill Prison in Plymouth. After two failed attempts at escape, both of which were foiled when Conyngham was recognised, he finally escaped and secured passage to Holland but was once more intercepted and imprisoned fourth time. This final bout in the Mill Prison would eventually result in his successful escape by bribing a guard.
The rest of Conyngham's fighting days were spent on dry land, as he fought tirelessly to clear his name of any wrong doing in Dunkirk. The original commission which could clear his name would, unfortunately, not be uncovered until almost 100 years after his death.