When John Quincy Adams—the sixty-three-year-old former president, U.S. senator, secretary of state, and diplomat—was elected to the House of Representatives by his Massachusetts neighbors, he embarked on a spectacular late-life career.

He became Congress’s most acerbic and influential critic of slavery as well as a tireless proponent for human freedoms and First Amendment rights. This remarkable congressional career utterly transformed him, the public’s perception of him, and his legacy—in many ways redeeming his failed presidency. Mr. Adams’s Last Crusade renders an insightful portrait of a man who placed his country above politics.