Edward P. Costigan graduated from Harvard University and was admitted to the bar, establishing a solid educational foundation and legal expertise. He spent several years in the private sector, including a period as a lawyer for various organizations, before transitioning to public service. Costigan held leadership roles in political and labor movements, such as chairing the Dry Denver Committee and serving as a lawyer for the United Mine Workers of America. His career included an appointment to the United States Tariff Commission and a tenure in the U.S. Senate, showcasing his ability to navigate both the legislative and regulatory landscapes.

Edward P. Costigan's political journey reveals a unique blend of ideological agility and localized advocacy, marked by an early shift from Republican to Progressive to Democrat. His labor advocacy, particularly during the Colorado coal strike, contrasts with his later economic policies favoring local option laws and honest elections. Costigan's legislative record shows an unexpected convergence with opposing factions on environmental regulations, revealing a highly calculated approach to protecting regional industrial interests.