Michael Newbold Castle (July 2, 1939 – August 14, 2025) was an American politician and lawyer who served as the U.S. representative for Delaware's at-large congressional district from 1993 to 2011. A member of the Republican Party, he previously served as the 69th governor of Delaware from 1985 to 1992, lieutenant governor from 1981 to 1985, and as a member of the Delaware General Assembly from 1967 to 1977. As of 2025, Castle is the most recent Republican to represent Delaware in the U.S. Congress and to have been elected governor of the state.
The district Castle represented includes the entire state of Delaware and is the oldest intact surviving district in the nation. He was the longest-serving U.S. Representative in the state's history.
On October 6, 2009, Castle announced his candidacy in the 2010 special election for the seat in the United States Senate held by Democrat Ted Kaufman. Kaufman, appointed by Governor Ruth Ann Minner to fill the vacancy created by Joe Biden (who resigned to become vice president of the United States), was not a candidate in the election. The election determined who would fill the balance of Biden's term, which ended on January 3, 2015. In one of the most surprising election results of 2010, Castle lost the Republican primary to Christine O'Donnell. He would have been heavily favored in the general election against Democrat Chris Coons, who defeated O'Donnell by 17 percentage points.
Michael Newbold Castle was born on July 2, 1939, in Wilmington, Delaware, the son of Louisa Johnston (née Bache) and James Manderson Castle Jr. One of his maternal great-great-grandfathers was Virginia U.S. Senator John W. Johnston, and Castle's fifth great-grandfathers were founding fathers Benjamin Franklin and Daniel Carroll. Castle's father was a patent lawyer for DuPont, a firm so central to the city that it was long known in Wilmington simply as "the company." After graduating from Tower Hill School in 1957, he attended Hamilton College in Clinton, Oneida County, New York. He earned a Bachelor of Science degree in economics from Hamilton in 1961. While at Hamilton, Castle was a brother of the Alpha Delta Phi fraternity.
In 1964, he earned a Juris Doctor degree from Georgetown University Law Center in Washington, D.C. He was admitted to both the Delaware Bar and the Washington, D.C., Bar that same year.
Professional and political career
Following his admission to the bar, Castle returned to Wilmington and joined Connolly, Bove and Lodge, working as an associate (1964–1973) and later partner (1973–1975). A Republican, he served as Deputy Attorney General of Delaware from 1965 to 1966, and was elected to the Delaware House of Representatives in 1966. He served as a state representative for two years before winning a seat in the Delaware Senate, where he remained for eight years. He also served as minority leader from 1975 to 1976.
In 1976, Castle left the state legislature and returned to the full-time practice of law, founding his own firm with Carl Schnee (who was later nominated as U.S. Attorney for the District of Delaware by President Bill Clinton in 1999). He returned to politics in 1980, when he was recruited to run for Lieutenant Governor of Delaware by Governor Pete du Pont. He defeated Democratic state senator Thomas B. Sharp, with 59% to 40% of the vote. He served from 1981 to 1985.
As the hand-picked choice of the popular Governor du Pont, Castle easily won election as Governor of Delaware in 1984, defeating former Delaware Supreme Court Justice William T. Quillen. Voters re-elected him to another term in 1988 when he defeated Democrat Jacob Kreshtool by 99,479 votes, and is the last time a Republican won a governor election in the state. Castle cut his second term slightly short when he resigned to begin his first term as U.S. Representative.
One of Castle's priorities as governor was welfare reform. He worked to pass a comprehensive welfare reform package with the White House and Congress and also served as lead governor on welfare reform on the National Governors Association. He worked on the largest road-construction project in state history, with his administration establishing the Transportation Trust Fund that paid for the construction of Delaware Route 1. He also worked on the improvement of schools, supported the preservation of farmland, and backed "banking industry expansion and anti-takeover legislation for corporations".
Committee on Education and Labor
Subcommittee on Early Childhood, Elementary and Secondary Education (Ranking Member)
Subcommittee on Higher Education, Lifelong Learning, and Competitiveness
Committee on Financial Services
Subcommittee on Capital Markets, Insurance, and Government-Sponsored Enterprises
Subcommittee on Financial Institutions and Consumer Credit
Subcommittee on Domestic Monetary Policy and Technology
In 1992, Castle could not run again for Governor, due to constitutional term limits. The result was what became known as "the Swap." Castle ran for the seat of U.S. Representative Tom Carper and Carper ran for Governor. Delaware's political leadership had quietly worked out the arrangement and retained the services of two very popular office holders. Both Castle and Carper won their races by large margins.