Joseph Aplin, the son of the lawyer John Aplin, was born in Rhode Island, and became a lawyer there himself. When the American Revolutionary War began, Aplin remained loyal to the British; his unpopular opposition to the rebels forced him to move, in 1775, to a more sympathetic loyalist area of the island, where he remained until 1780. He was apparently unable to practice law during that time. Aplin was four times arrested by the rebel military because of his outspoken support of the British. In 1780 he fled to the British held colony of New York; it is likely that he met the DeLancey family there. In December of 1783, when the British lost control of the colony, Aplin, along with many other Loyalists (including James DeLancey) moved to Nova Scotia.

Aplin became involved in the politics of the British colonies in Nova Scotia and New Brunswick. He was part of a movement that advocated the separation of New Brunswick and Nova Scotia; in 1785 he was elected to the Nova Scotia House of Assembly. When Edmund Fanning, a former Lieutenant Governor of Nova Scotia, became Lieutenant Governor of Prince Edward Island (at the time called St. John's Island) in 1787, Aplin joined him there as solicitor general. His involvement in the politics of the island proved controversial, eventually leading to his downfall.

Aplin supported Fanning in urging the reinstatement of former chief justice Peter Stewart, who had been suspended by Walter Patterson, the previous lieutenant governor of the island. In 1788 Aplin worked with the attorney general of the island in revising the colony's laws; in 1790 Aplin was appointed attorney general himself. Island politics of the time was dominated by a feud between the Fanning-Stewart faction, with which Aplin was identified, and the supporters of Walter Patterson. The feud apparently did not remain political; in 1790 Aplin was seriously wounded by a Patterson party adherent. In 1791 the Patterson party brought charges of malfeasance to the Privy Council in London against Aplin, Fanning and Stewart. The charges were dismissed in 1793 and Aplin successfully sued his persecutors for malicious prosecution.

Despite all this, Aplin was not much concerned with local politics, saying that the party differences were not “worth quarreling about” and “Sore Enemies” to his “Peace of Mind.” Though he was thought to be a supporter of the Fanning-Stewart party, by 1797 Aplin had become part of a group critical of Fanning and Stewart, who were then involved in a controversy over provincial land. The group proposed the joining of Prince Edward Island and Nova Scotia, claiming that the island province was too small to attract "responsible" officials. This stance resulted in Aplin being charged by his new enemies with legal malpractice and sedition, and he was dismissed from the post of attorney general.

In debt and unable to work as a lawyer, Aplin fled to England in 1798, where he continued to advocate the joining of the two provinces while trying to clear himself of the charges against him. In this he was unsuccessful, at least in part because of his "rash" statements against Fanning, who he accused of being either a “tame dupe” or a wielder of “misapplied power”. Running out of money, Aplin returned to Nova Scotia to resume his law practice in Annapolis Royal.

It would have been after this, in 1800 or 1801, that he provided his lengthy legal opinion supporting DeLancey's case against Woodin. Aplin's opinion was cited in 1806, in a New Brunswick case similar to DeLancey vs. Woodin, where a man named Samuel Street was accused of harboring a runaway slave. The judge in the case dismissed Aplin's opinion:

"[The defense council stated that] the action of Trover would not lie for a Negro Slave, because no person could have that uncontrolled and unlimited property in a Slave, which was necessary to support this action. The Counsel for the Plaintiff urged in reply, that an action like this had been brought in Nova Scotia by Mr. De Lancey, and quoted the opinion of Mr. Aplin, supported by several learned Gentlemen in England, (as appeared in a Pamphlet published in this Province,) but the Chief Justice did not think that case of sufficient authority, and directed the Nonsuit..." - "Biographical Information on Ward Chipman", University of New Brunswick libraries web site.

Some time before his death in 1804, Aplin apparently returned to his native land of Rhode Island, where his death was reported in a local newspaper in that year.

Biography of
Joseph Aplin (1740-1804)