Blanchard was born in Detroit, Michigan and attended the public schools of Ferndale. He received a B.A. from Michigan State University in 1964 and an MBA from the same university in 1965. He received a J.D. from the University of Minnesota Law School in 1968 and was admitted to the Michigan bar in the same year. He commenced practice in Lansing and served as legal advisor to the Michigan Secretary of State, 1968-1969. He was Assistant Attorney General of Michigan, 1969-1974, administrative assistant to the attorney general, 1970-1971, and assistant deputy attorney general, 1971-1972.

Blanchard was elected as a Democrat to the United States House of Representatives from Michigan's 18th District for the Ninety-fourth and to the three succeeding Congresses, serving from January 3, 1975 to January 3, 1983. He was not a candidate for reelection in 1982 but was elected Governor of Michigan, defeating Republican state representative Richard Headlee. Blanchard served two terms as governor (1983-1991) until his defeat by Republican state senator John Engler in 1990.

Blanchard became embroiled in a bitter partisan dispute over an appointment to the Michigan Supreme Court. On December 9, 1982, outgoing Republican Governor William Milliken appointed Dorothy Comstock Riley to the Michigan Supreme Court to fill the vacancy caused by the death of Justice Blair Moody on November 26. Since Milliken was leaving office in less than a month, the governor-elect Blanchard argued he should have made the appointment to replace Moody rather than Milliken. Further complicating the matter, Riley had run for election to the Supreme Court in the 1982 general election and had been defeated. In February 1983, the other Supreme Court Justices voted 4-2 to remove Riley from the court. Blanchard replaced her with U.S. District Court Judge Patricia Boyle. However, Riley won election to the Supreme Court in 1984.

President Bill Clinton appointed him Ambassador to Canada, a position he held from 1993 to 1996. In 2002 Blanchard again ran for governor but lost his primary bid to Jennifer Granholm. As of 2004, he is a partner in the Washington D.C. law firm of Piper Rudnick and resides in Pleasant Ridge.

Preceded by: Robert J. Huber United States Representative for the 18th Congressional District of Michigan 1975-1983 Succeeded by: William S. Broomfield Preceded by: William Milliken Governor of Michigan 1983-1991 Succeeded by: John Engler Preceded by: Peter Teeley Ambassador to Canada 1993-1996 Succeeded by: George D. Giffen