From the late 1950s until the early '80s, Mr. McMahan served as an outspoken ad critic, writing a column for Advertising Age and speaking on a worldwide lecture circuit. Starting in 1961, he annually picked the nation's 100 Best TV Commercials.
"He was knowledgeable, witty and never shy about telling it like it is," said Fred Danzig, Advertising Age contributing editor. "For years, Harry packed hotel ballrooms with advertising people in every major city. Many a creative career, and ad agency, blossomed by virtue of Harry's reel and his column."
Ed Ney, chairman of the board of advisers at Burson-Marsteller, New York, a division of Young & Rubicam, remembered Mr. McMahan as a "one-man professorial band" who made "great contributions to advertising." He taught the world about good advertising, Mr. Ney said.
Before becoming a columnist and consultant, Mr. McMahan worked at Leo Burnett USA, Chicago, and McCann-Erickson Worldwide, New York.
For the past 15 years, he lived in California and worked on some publishing projects.
"He lived and loved advertising," said his wife, Gloria.
Mr. McMahan had suffered from Alzheimer's disease for the past five years.