He graduated from Dartmouth College in 1804, studied law with Chief Justice Theophilus Parsons, and became an eminent lawyer. During the War of 1812, he commanded a regiment of militia on the coast defences.
He was a representative in the Massachusetts legislature from 1812 to 1816. Knapp was elected a member of the American Antiquarian Society in 1814. In 1816, he was imprisoned for debt, upon his release from prison in 1817, he moved to Boston.
He became editor of the Boston Gazette in 1824, also conducting the Boston Monthly Magazine. In 1826 he established the National Republican, which failed two years later, and he returned to practicing law in New York City. He was given the degree of LL.D. from the Paris College.
Abby Jane Morrell
Narrative of a voyage to the Ethiopic and South Atlantic Ocean, Indian Ocean, Chinese Sea, North and South Pacific Ocean, in the years 1829, 1830, 1831
His works, which are chiefly biographical, include:
"Ali Bey," Extracts of a Journal of Travels in North America, consisting of an account of Boston and its vicinity (Boston, 1818). A burlesque imitation of Travels of Ali Bey in Morocco… (Ali Bey in this second work being a pseudonym for Domingo Badia y Leblich; 2 vols., Philadelphia, 1816); Knapp's 1818 work purports to give an oriental traveler's experiences of society in Boston and Cambridge.
Biographical Sketches of Eminent Lawyers, Statesmen, and Men of Letters (1821)
"Ignatius Loyola Robertson," Sketches of Public Characters (1830)
American Biography (1833)
Narrative of a Voyage to the Ethiopic and South Atlantic Ocean, Indian Ocean, Chinese Sea, North and South Pacific Oceans, in the Years 1829, 1830, 1831 was published in New York in 1833 by J. & J. Harper. Ghost-written by Knapp it re-told the experience of merchant's wife and explorer Abby Jane Morrell.
History of the United States, a revised edition of a work by John Hinton (1834)
He edited "The Library of American History" (New York, 1837). He was the author of a variety of occasional public addresses. George Harvey Genzmer, in evaluating his biographies in the Dictionary of American Biography, calls him "ornate, laudatory, and patriotic, and wholly untrustworthy."
^ George Frisbie Whicher, "Early Essayists," Book II, Chapter III, in William Peterfield Trent, John Erskine, Stuart P. Sherman, and Carl Van Doren, eds., The Cambridge History of American Literature, 1917-1921.