Alan Dixon, a former U.S. senator who died July 6 at age 86, was chairman of the Base Closure and Realignment Commission in the mid-1990s. (Dennis Cook/AP)

Former U.S. senator Alan Dixon, an Illinois Democrat whose career in national and state politics spanned more than 40 consecutive years in public office, died July 6 at his home in Fairview Heights, Ill. He died the day before his 87th birthday.

His son Jeffrey Dixon confirmed the death but did not disclose the cause.

After being elected police magistrate in Belleville, Ill., Mr. Dixon won an Illinois House seat in 1950. He went on to serve in the Illinois Senate and as the state’s treasurer and secretary of state. He won his U.S. Senate seat in 1980 and served there until his surprising loss in the 1992 Democratic primary to Carol Moseley Braun.

In the Senate, Mr. Dixon served as the third-ranking Democrat and chaired a subcommittee of the Armed Services Committee.

Among Mr. Dixon’s more controversial moves — which later led to his defeat — was voting to support the nomination of Clarence Thomas to the Supreme Court in 1991 after law professor Anita Hill said Thomas sexually harassed her.

Braun, who had served as a Cook County, Ill., recorder of deeds, said she challenged Mr. Dixon because of her outrage over the treatment of Hill during the confirmation hearings. Braun was the first African American woman to serve in the Senate.

Mr. Dixon later defended his vote by saying Thomas was qualified and that he doubted Hill, according to his 2013 memoir, “The Gentleman from Illinois.”

He described other factors leading to his loss, including a sluggish economy and a 1992 banking scandal involving some U.S. House members that generated negative feelings toward public officials in general.

“All of these matters contributed to some extent to the perfect storm undercutting my primary campaign,” he wrote in the book. “Having said this, though, I want to emphasize that my basic undoing was the loss of my traditionally liberal base and certain active women’s organizations as a result of my Clarence Thomas vote. No amount of explanation for my vote satisfied these groups.”

Alan John Dixon was born July 7, 1927, in Belleville and served in the Navy Air Corps in 1945. Later, he graduated from the University of Illinois and Washington University law school in St. Louis.

He returned to practicing law after his 1992 reelection loss.

Survivors include his wife, Jody, and three children.