As of 2019, which U.S. senate is the longest-serving representative in U.S. history?

John David Dingell Jr. (July 8, 1926 – February 7, 2019) was an American politician who served as a member of the United States House of Representatives from 1955 until 2015. A member of the Democratic Party, he holds the record for longest-ever serving member of Congress in American history, representing Michigan for more than 59 years. He most recently served as the representative for Michigan's 12th congressional district. A longtime member of the House Energy and Commerce Committee, Dingell was the chairman of the committee from 1981 to 1995 and 2007 to 2009.

Dingell began his congressional career by succeeding his father, John Dingell Sr., as representative for Michigan's 16th congressional district on December 13, 1955; his father had held the seat for 22 years. He left office on January 3, 2015. Having served for over 59 years, he has the longest congressional tenure in U.S. history. He was also the longest-serving Dean of the U.S. House of Representatives and Dean of the Michigan congressional delegation. During his time in Congress in addition to protecting the automobile industry important to his district, Dingell was instrumental in passage of the Medicare Act, the Water Quality Act of 1965, Clean Water Act of 1972, the Endangered Species Act of 1973, the Clean Air Act of 1990, and the Affordable Care Act, among others. He was most proud of his work on the Civil Rights Act of 1964.