Mark Shields, a longtime TV political pundit and syndicated columnist in Washington known for his expansive knowledge of U.S. politics, humor and staunch support of liberal Democrats, died on Saturday at age 85.

Shields, who provided insights on six presidential administrations, died from complications of kidney disease, his daughter, Amy Doyle, told the Washington Post.

He is perhaps best known to the public as a commentator for PBS, where he spent nearly two decades on the PBS NewsHour program sparring with David Brooks, a conservative political commentator and columnist for the New York Times.

Judy Woodruff, the anchor and managing editor of the NewsHour, wrote on Twitter that she was heartbroken with the news that "Mark Shields, who for decades wowed us with his encyclopedic knowledge of American politics, his sense of humor and mainly his big heart, has passed away."

When Shields retired two years ago, Brooks dedicated a column in the Times to his rival. "We've had thousands of disagreements over the years, but never a second of acrimony. Mark radiates a generosity of spirit that improves all who come within his light," Brooks wrote.

Shields was a native of Weymouth, Massachusetts and fiercely proud of his Irish-American roots and Roman Catholicism.

Before he became a fixture on the political airwaves, where he matched wits with conservatives, Shields served as a U.S. Marine for two years. He attended the University of Notre Dame and later spent a decade on Capitol Hill and worked on campaigns for Democrats including former Senator Robert F. Kennedy's 1968 presidential bid.

Shields was also a frequent panelist on Inside Washington, a weekly public affairs show that ran on PBS and ABC. Shields was also a moderator and panelist on CNN's Capital Gang for 17 years.

News accounts say he died at his home in Chevy Chase, Maryland, with his wife Anne at his side.