Born in Baltimore, he was the son of a grocer. The family lived on West Lanvale Street and on White Chapel Road in the Ashburton section of Northwest Baltimore.
He was a 1940 graduate of City College, where he performed in shows. During World War II, he served in the Army Air Corps and was stationed in Calcutta, India.
After the war he earned a bachelor's degree in 1950 at the University of Maryland, College Park, where he also performed in theatrical productions.
After working at the Criminal Investigation Division of the Maryland State Police and spending a summer as a camera operator at Baltimore's WAAM-TV, he moved to Philadelphia. He studied advertising there and then moved to New York, where he took a job as secretary with the William Morris Agency.
According to a 1975 Baltimore Sun story, Mr. Platt immersed himself in show business and worked on Sid Caesar's "Show of Shows," "The Colgate Comedy Hour" and the Danny Thomas, Martha Raye and Red Buttons television shows.
At the Morris agency, he met Hillard Elkins, an agent who taught him show business management. Mr. Platt's early assignments included Phyllis Diller, Carroll O'Connor, Bea Arthur and Neil Simon.
He soon became a personal manager for Steve McQueen, Robert Culp, songwriters Charles Strouse and Lee Adams and librettist Michael Stewart.
Working alongside Mr. Elkins, who concentrated his work on the West Coast, Mr. Platt remained in New York and focused on television, property development and theater.
"He was Hilly's right-hand man, indispensable in many ways," said Bill Liberman, a former associate and friend who lives in New York. "He was competent and had an amorphous job. He was a warm and friendly guy."
In 1962, when Mr. Elkins began his production company, Mr. Platt served as his assistant in the Garson Kanin production of "Come on Strong" starring Van Johnson and Carroll Baker, and then as associate producer for "Golden Boy," starring Sammy Davis Jr. The show ran for nearly two years on Broadway.
Mr. Platt liked telling theatrical stories, including that of a doctors' answering service that began broadcasting over the same frequency as a wireless mike strapped to Sammy Davis' chest. He also worked with the NECCO candy firm to have a Golden Boy chocolate bar made. It was a commercial failure.
"He talks in fast, yet rambling sentences that rarely get finished in his exuberance to embark upon the next thought," said the 1975 profile of him in his Broadway years.
He also helped create the musical "The Rothschilds" starring Hal Linden, Jill Clayburgh, Robby Benson and Chris Sarandon.
"It took us six years to get the show into production," he said in a 1981 Sun article when "The Rothschilds" was revived at Baltimore's Jewish Community Center. "The reason? We couldn't get a script. New York is full of writers, but, that's right, we couldn't get a decent script."
He was also an associate producer on the long-running avant-garde revue "Oh! Calcutta," and produced a television special for jazz clarinetist Benny Goodman.
In 1973, he changed careers after his business partner, Mr. Elkins, moved his office out of New York. Mr. Platt moved his family to Baltimore and became sales promotion director for a family-owned wholesale lawn and garden business, the David Platt Co. He retired nearly 25 years ago.
In his free time, he baked cakes and brownies. He read newspapers and followed baseball and football on television.
Graveside services will be held at 2 p.m. Wednesday at Columbia Memorial Park, 10632 Little Patuxent Parkway in Columbia.
Survivors include his wife of 53 years, the former Phyllis Diamond; two daughters, Dara O'Malley of Rodgers Forge and Melissa Campbell of Pinehurst; a brother, David Platt of Pikesville; a sister, Anne Siegel of Stamford, Conn.; and five grandsons.