In 1986, he began writing for Show Music magazine[1] and the New York Native, and the following year he joined the staff of TheaterWeek.[2] He was a frequent contributor to Playbill and wrote a regular column for Broadway.com until 2006. Before his career as a theatre writer, he was a teacher in New York public schools.
The New York Times called Not Since Carrie a "must read", saying, "Mr. Mandelbaum hits all the highlights, everything from Breakfast at Tiffany's,' starring Mary Tyler Moore as Holly Golightly, to last season's Shogun: The Musical. Mr. Mandelbaum also takes a good swipe at Annie 2: Miss Hannigan's Revenge."[5]