The hit show Baker Street (it ran 311 performances) was a musical telling of the adventures of famed fictional detective Sherlock Holmes. The show was an early directorial effort by Harold Prince and starred Fritz Weaver as a speak-singing Holmes, a la Rex Harrison in My Fair Lady. Raymond Jessel shared scoring duties with Ms. Grudeff. She is credited as being the first Canadian to pen a Broadway show.

"Marian was an immensely enthusiastic person," Jessel told the Toronto Star, "but she would never let me get away with second-best. She was an impeccable musician and also was very fussy about the way our words went. ... She was magical when she was at the piano singing the songs of Rodgers and Hart."

Ms. Grudeff and Jessel met when she became the musical director of Toronto's Spring Thaw, a musical comedy revue. They went on to write Hellzapoppin' for Expo '67 in Montreal, and the musical Life Can Be—Like Wow for the Charlottetown Festival in 1969.

Born in Toronto, Ms. Grudeff was a child prodigy. She made her concert debut at 11 with the Toronto Symphony Orchestra at Massey Hall. Her concert career included appearances at Town Hall and Carnegie Hall in the 1950s. In recent years, she worked with Don McKeller, Bob Martin and Lisa Lambert—the creators of Broadway’s The Drowsy Chaperone—on sketches and songs for Toronto Fringe shows.

Ms. Grudeff is survived by her son, Christopher McDonald, and her sister Lillian Grudeff.