A self-described “Southern liberal” steeped in New Deal politics, Mr. McPherson was a Washington legal mandarin at the center of the capital’s power elite for decades. He spent his post-White House years with what became Verner, Liipfert, Bernhard, McPherson and Hand — a practice he helped transform into one of the District’s prominent lobbying shops.

Verner, Liipfert merged in 2002 with what is now DLA Piper, and Mr. McPherson worked there until 2010. As one of the firm’s “wise men,” he helped represent media companies, airlines and foreign governments. In the late 1990s, he played a public role in the firm’s efforts to help leading tobacco manufacturers reach a settlement with the government over smoking-related lawsuits.

Long after he left the Johnson administration, Mr. McPherson remained a presence in the District’s political, cultural and civic life. He wrote a memoir, “A Political Education” (1972), that remains among the most enduring portraits of power in the capital, seen at first from the fringes when he was a newcomer from Texas and then from the epicenter at the White House.

Louis Lyons, the late journalist and curator of Harvard University’s Nieman Foundation, reviewed “A Political Education” for the Christian Science Monitor and called it “a portrait of a man gifted with extraordinary insight and the capacity to put politics in perspective, and with an appreciation of the humanity and commitment of public men, striving through frustrations and fickleness to make democracy work.”

“A Political Education” piquantly detailed the clay feet of nearly everyone in politics he had met. Mr. McPherson did not spare himself, noting moments when he lost sight of his “political morality” in the desire to please charismatic leaders.

In the crucible of the White House, Mr. McPherson developed strong reserves of forbearance working for a president who favored a “bear-pit school of personnel management.” Johnson enjoyed keeping underlings off balance with his sharp temper and demanding ways. Nonetheless, Mr. McPherson deeply admired Johnson’s adroit political instincts and his colorful way of expressing them.

To Johnson, powerful lawmakers were “whales,” and he needed but a few to succeed in any legislative showdown. He once castigated Mr. McPherson for having rounded up “all the minnows.”

Over time, Mr. McPherson said he came to regard a certain detachment — a balance of “fervor and humor” — as crucial personality traits for anyone hoping to succeed in Washington.

An aspiring poet in his youth, Mr. McPherson changed his professional ambitions in the early 1950s when he felt an ardent passion to defend those being targeted by Sen. Joseph McCarthy (R-Wis.) as communist sympathizers. “I was worried that he was going to usher a period of totalitarianism in the United States,” Mr. McPherson told an interviewer in 1999.