In his one bid for elective office, Williamson lost a 1992 race for the U.S. Senate to Carol Moseley Braun, D-Ill.
The Republican Party in Illinois announced that Williamson died Sunday after suffering a cerebral hemorrhage, the Chicago Tribune reported.
Williamson advised Republican presidents and presidential candidates from Ronald Reagan to Mitt Romney. He served in a variety of diplomatic jobs under Reagan, George H.W. Bush and George W. Bush, including assistant secretary of state, ambassador to the United Nations office of human rights and special envoy to the Sudan.
In 2012, he described Obama's foreign policy as "amateur hour."
Romney said Williamson was "a man of conviction, courage and consistency."
"The nation has lost a noble patriot and I have lost a dear friend," he said.
Williamson grew up in Evanston, Ill., and graduated from Princeton and the University of Virginia law school. He practiced law in Chicago but also became involved in Republican politics with Reagan's 1976 campaign, when the future president failed to topple President Gerald Ford.
In 1992, Williamson was tapped for a sacrificial candidacy against U.S. Sen. Alan Dixon, D-Ill. When Braun, who became the first black woman in the U.S. Senate, defeated Dixon in the Democratic primary, Williamson was in the spotlight.
Williamson admitted he was uncomfortable as a candidate, saying he was not "someone who thrusts their hands into the faces of strangers."
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