He has worked with Carole King[1] (appearing on six of her albums as a performer and producer), Ani DiFranco, and Eliza Gilkyson.
Navarro put out two albums on Capitol Records, Listen in 1977 (produced by Hallman) and Straight From the Heart in 1978.
Although Navarro had broken up by the time King called, she asked Hallman if the band would like to back her for an album on Lou Adler's Ode Record label.
The song "Glass House," co-engineered by Hallman off of DiFranco's 1999 CD Little Plastic Castle was nominated for a Grammy in 1998 for Best Female Rock Vocalist.
A feature-length film, The Shopkeeper: A Documentary about Mark Hallman & the Music Business, produced by Rain Perry, was released in 2016.