Delahunt came to Congress in 1997 with a distinguished career in public service and law enforcement. For fourteen years, he represented the Tenth Congressional District of Massachusetts. In Congress he served as a member of the House Judiciary Committee and the House Foreign Affairs Committee, and recently served as the Chairman of its Subcommittee on Europe. Prior to his service in Congress, Delahunt was a District Attorney in the metropolitan Boston area for twenty two years. He is known for having developed the country's first prosecutorial unit on domestic violence and sexual assault cases. Delahunt pioneered programs to combat violence against women that have become national models. Delahunt's ability to work with both political parties helped play a pivotal role in the passage of several legislative proposals he authored, including the Justice for All Act and the Travel Promotion Act and legislation streamlining international adoptions. Delahunt also introduced the first House proposal to establish the Consumer Financial Protection Agency, which was eventually incorporated into the final Financial Reform law enacted in 2010.

Oil and gas industry