John McLaughlin, a former Roman Catholic priest who became an aide to Richard M. Nixon in the White House and parlayed his fierce defense of the president into a television career as host of “The McLaughlin Group,” the long-running Sunday morning program of combative political punditry, died on Tuesday at his home in Washington. He was 89.

His death was announced on the program’s Facebook page. The columnist Eleanor Clift, a longtime panelist on the show, wrote in The Daily Beast that he had been treated for prostate cancer for some time and that it had spread.

Mr. McLaughlin had been absent from the show this last weekend for the first time in more than 34 years. “I am under the weather,” he wrote to viewers in a note that began the broadcast, adding that his voice was “weaker than usual” but that his “spirit is strong.”

As creator, executive producer and host of “The McLaughlin Group,” which began in 1982, Mr. McLaughlin helped reinvent the political talk-show format by injecting unabashed partisanship and a dash of entertainment.