In 1927, Morris began teaching History at the City College of New York until in 1946 he was named to the faculty of Columbia University, after having published Government and Labor in Early America (1946).

[1] Morris was privately opposed to the Columbia University protests of 1968 and the agenda of the radicals, but made no public statements on the matter.

Morris's own contribution to the Bicentennial, and the culmination of his life's work as a historian, was The Forging of the Union, 1781–1789, his 1987 volume for the New American Nation series.

[1] Columbia University colleague Henry Steele Commager enlisted Morris as co-editor of the influential New American Nation series, a collaborative history of the United States published by Harper & Row.

In 1973, preparing for the impending bicentennial of the American Revolution, he published Seven Who Shaped Our Destiny: The Founding Fathers as Revolutionaries, a collection of biographical essays about Benjamin Franklin, George Washington, John Adams, Thomas Jefferson, John Jay, James Madison, and Alexander Hamilton.