He studied law, was admitted to the bar in 1852 and practiced in Pittsburgh, Pennsylvania, for twenty years.

For several years he served as vice president of the Pittsburgh chamber of commerce.

He served as the chairman of the United States House Committee on Labor during the Forty-eighth Congress.

He introduced the first (successful) bill implementing federal regulations on interstate commerce in 1872.

Muckraker Ida Tarbell cites Hopkins in many of her works and speeches.