Democrats and Southern Whigs favored the rule, but Northern Whigs, like Adams, opposed it.[202] In late 1836, Adams began a campaign to ridicule slave owners and the gag rule. He frequently attempted to present anti-slavery petitions, often in ways that provoked strong reactions from Southern representatives.[203] Though the gag rule remained in place,[204] the discussion ignited by his actions and the attempts of others to quiet him raised questions of the right to petition, the right to legislative debate, and the morality of slavery. Adams fought actively against the gag rule for another seven years, eventually moving the resolution that led to its repeal in 1844.[205]

Adams's portrait at the U.S. National Portrait Gallery by George Bingham c. 1850 copy of an 1844 original
In 1841, at the request of Lewis Tappan and Ellis Gray Loring, Adams joined the case of United States v. The Amistad. Adams went before the Supreme Court on behalf of African slaves who had revolted and seized the Spanish ship Amistad. Adams appeared on February 24, 1841, and spoke for four hours. His argument succeeded: the Court ruled that the Africans were free and they returned to their homes.