Marcus, originally from Pittsburgh, was educated at George Washington University in Washington, D.C. She has been active as a theatrical photographer in Washington, D.C. and New York City for most of her career. Starting in 1986, she has been a photographer on Broadway theatre productions, covering over a hundred shows including Wicked, The Lion King, SisterAct, and The Book of Mormon. She is considered to be "one of the preeminent Broadway photographers." Joan Marcus is married to the theatrical press agent Adrian Bryan-Brown of Boneau/Bryan-Brown, a leading Broadway press agency.