By Sam Roberts

Doug Kendall, a liberal lawyer and co-author of dozens of United States Supreme Court briefs challenging the prevailing conservative vision that the Constitution defines the federal government’s jurisdiction narrowly, died on Saturday at his home in Washington. He was 51.

The cause was colon cancer, according to the Constitutional Accountability Center, a Washington research organization and public-advocacy law firm, which he founded in 2008.

Mr. Kendall saw the center as a counterweight to the conservative ascendancy on the Supreme Court, where justices like Antonin Scalia, Clarence Thomas and Samuel Alito have sought to interpret the Constitution on the basis of the framers’ original intent.

Drawing on the scholarship of Yale Law School professors including Akhil Reed Amar and Jack M. Balkin, Mr. Kendall sought to use the conservatives’ own judicial strategy on behalf of liberal aims.

“Progressives are losing the fight over the courts and the Constitution because conservatives have maneuvered us into running from, rather than embracing, the text and history of the Constitution,” Mr. Kendall and Jim Ryan, a University of Virginia law professor, wrote in 2011 in the journal “Democracy.”

“The Constitution, we’ll often find,” they concluded, “is on our side.”

When California was sued over environmental regulations that were stricter than protections imposed by federal law, Mr. Kendall, in asserting the rules’ constitutionality, borrowed from conservative arguments defending federalism and states’ rights.

In another case, he strategically joined conservatives in a brief opposing a gun control law in Washington, D.C., invoking the 14th Amendment’s “privileges and immunities” clause, which protects citizens’ rights against local government infringement.

Then he turned around to argue that the same amendment protecting a citizen’s right to bear arms in a particular locality, as granted under the Second Amendment, can also be the legal underpinning of civil rights laws that the federal government imposes on localities.

“Even where I disagree with their conclusions, the briefs and arguments submitted by the Constitutional Accountability Center make a vital contribution to the adversary process by which claims of original meaning should be vetted,” Prof. Randy Barnett of Georgetown University Law Center, a frequent conservative adversary who joined him in the gun control brief, wrote on Sunday on a legal blog on The Washington Post website.

Mr. Kendall argued publicly, in judicial nomination hearings and before the courts, on behalf of affordable health care, voting rights, fair housing, marriage equality and other causes, insisting all the time that the framers were not “a group of gun-toting, property-loving and tax-hating defenders of big corporations and proponents of small government,” as he wrote in the journal “Democracy.”

“Doug played a critical role in the defense of the Affordable Care Act by marshaling the best arguments in his own briefs and skillfully working to coordinate the efforts of others,” Walter E. Dellinger, a former assistant attorney general and adviser to the Constitutional Accountability Center.

Eschewing “living constitutionalism” and “original intent,” Mr. Kendall favored another theory called “new textualism.”

“New textualists believe that while the meaning of the Constitution does not change, application of those principles can lead to different outcomes as circumstances change,” he wrote in 2011 on the center’s blog.

Douglas Townsend Kendall was born in Huntington, on Long Island, on July 3, 1964. His father, George, was a salesman for a laser manufacturer. His mother, the former Judith Townsend, was a teacher.

He graduated from the University of Virginia, where he also earned his law degree.

Mr. Kendall practiced at Crowell & Moring in Washington and the National Environmental Trust before founding his public advocacy firm.

The Constitutional Accountability Center evolved from Community Rights Counsel, an environmental law firm, which Mr. Kendall founded in 1997 and which exposed potential conflicts of interests posed by judges’ stock holdings in energy corporations and junkets subsidized by industry groups.

His survivors include his wife, Juliet McKenna, an associate judge on the Superior Court of the District of Columbia; their daughter, Miracle; and two siblings, George Kendall and Carolyn Townsend Stoller.