He served as head of the legal committee of the National Association for the Advancement of Colored People (NAACP) and was one of its vice presidents from 1911.
He interrupted his legal career to serve for several years as a United States Army captain in the Sanitary Corps during World War I and protested racial discrimination treatment of African Americans in the US military.
One of them was of books, newspapers, and manuscripts on the black American experience worldwide that was "unique in its depth, breadth, and quality.
At his memorial service, he was eulogized by Associate Supreme Court Justice Thurgood Marshall and Roy Wilkins, executive director of the NAACP.
Buell C. Gallagher, retired president of the City College of New York, called him "the rallying center of the aggressive forward movement" of the NAACP.