They had seven children: Margaret May, James Hunter, Daniel Calhoun Jr., Grace Henrietta, John Wesley Roper II (future Vice admiral), Harry McKenzie (future Major general) and Richard Frederick Roper.

From 1900 to 1910, he worked for the Census Bureau, and then served as the clerk of the Committee on Ways and Means in the U.S. House of Representatives from 1911 to 1913.

Immediately following and through 1916, he served as first assistant postmaster general, and was chairman of Woodrow Wilson's reelection campaign in 1916.

Roper's Letter of Credence was accepted personally by George VI, King of Canada, at La Citadelle in Quebec City, on May 17, 1939.

[2] Roper resigned effective August 20, 1939; the Roosevelt administration explained that his appointment was intended to be temporary, and had been made to ensure that the U.S. would have an ambassador in Canada when the king visited.