Cohan passed away on Wednesday in Pacific Palisades, California after suffering complications from large cell lymphoma, reports Daily Variety.
The screenwriter began his career as an assistant director/stage manager at U.S. TV network ABC before being drafted into Universal Television's documentary division.
He moved into sitcoms in the 1970s, writing for programmes including The Odd Couple, The Mary Tyler Moore Show and All In The Family. He also directed, produced and wrote episodes of The Bob Newhart Show.
He and his partner Blake Hunter created the Tony Danza series Who's The Boss? in 1984, and also co-created Silver Spoons.
Who's The Boss? star Judith Light has paid tribute to Cohan in a statement which reads: "Marty was such a rare treasure in our business: not only brilliant and funny but with a huge heart and unfailingly kind."
He is survived by his wife Dawn, a son and daughter, two stepchildren and a sister.