By Emily Langer

Doug Kendall, a litigator and activist who challenged conservative and even some liberal legal traditions by promoting the view that the Constitution is an essentially progressive founding document, died Sept. 26 at his home in Washington. He was 51.

His death, from complications of colon cancer, was announced by the Constitutional Accountability Center, a Washington-based think tank, law firm and advocacy group that Mr. Kendall established and led since its founding.

Historically, constitutional debate has created two broadly defined camps: a conservative one, favoring “originalist” theory hewing to what is believed to have been the intent of the Founding Fathers, and a liberal one, advocating the view that the Constitution is a “living document” that must be interpreted in the context of a dynamic and shifting society.

Mr. Kendall adopted and then helped advance another legal framework, in which originalist readings of the Constitution could produce liberal conclusions.

Jeffrey Rosen, the president of the National Constitution Center and a law professor at George Washington University, described Mr. Kendall as “the most important advocate in the public square for a vision of progressive originalism.”

“Doug Kendall had a vision,” Rosen said in an interview, “and that was that liberals and progressives — by making arguments rooted in constitutional text and history — could persuade open-minded conservative and libertarian judges of the correctness of their position.”

“It was an idealistic vision; it was a bipartisan vision,” Rosen said, and “it took seriously the idea that there are constitutional arguments that transcend politics.”

Mr. Kendall established the Constitutional Accountability Center in 2008. The center’s central conviction, according to its Web site, is “that the Constitution is, in its most vital respects, a progressive document, written by revolutionaries and amended by those who prevailed in the most tumultuous social upheavals in our nation’s history.”

The center weighed in with briefs and arguments on a range of legal matters, including affirmative action, voting rights, same-sex marriage, campaign spending by organizations, health care and immigration.

In Padilla v. Kentucky, a case involving a Honduran immigrant who pleaded guilty to trafficking marijuana not realizing that the decision would probably result in his deportation, the center compared deportation to banishment, which the framers of the U.S. Constitution regarded as one of the most stringent of criminal penalties.

In 2010, the U.S. Supreme Court ruled 7 to 2 that lawyers who represent immigrants must advise their clients when a guilty plea might result in deportation.

Douglas Townsend Kendall was born in Huntington, N.Y., on July 3, 1964. He received a bachelor’s degree in economics in 1986 and a law degree in 1992, both from the University of Virginia.

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Early in his career, Mr. Kendall practiced with the firm Crowell & Moring in Washington and with the National Environmental Trust, a nonprofit organization. In 1997, he founded the Washington-based Community Rights Counsel, which sought to defend environmental-protection legislation using traditionally conservative legal arguments.

“I became convinced that the same approach could be employed in a much broader range of disputes,” he told the New Republic magazine in 2012, explaining why he founded the Constitutional Accountability Center in 2008.

Survivors include his wife of 17 years, Juliet McKenna of Washington; a daughter, Miracle Kendall of Washington; a brother; and a sister.