Hoar may be best known in American history for his 1844 trip to Charleston, South Carolina as an appointed Commissioner of the state of Massachusetts. He went to South Carolina to investigate and contest the laws of that state, which allowed the seizure of sailors who were free African Americans (often who were citizens of Massachusetts) and placed into bondage, if such sailors disembarked from their ship. Hoar was prevented from undertaking his appointed tasks by resolutions of the legislature and efforts of the governor of South Carolina, and was escorted back onto a ship by Charleston citizens fearing mob violence against the agent from Massachusetts. News of the thwarting of Hoar inspired anti-slavery political reaction in Massachusetts.