His work has been influenced alike by John Adams, Olivier Messiaen, Magnus Lindberg, Joni Mitchell, the old American blues and folk field recordings of the Lomaxes, and the giants of post-Partch American microtonality such as Ben Johnston and James Tenney. For two years he was the co-director of Formerly Known as Classical, a San Francisco Bay Area new music ensemble whose young members play only music written in their lifetimes, and he is now the co-artistic director and co-founder of Contemporaneous, a New York new music ensemble. He performs frequently as a cellist, bassist, pianist, guitarist, and singer.

Mattingly is also a painter, playwright, and a pitcher for Bard College's club baseball team. In the past he has played cello in an improv string quartet called the Superdelegates and was guitarist and vocalist in the blues/funk/classic rock band Funky Bus & the U-Turns. He is currently part of the multi-instrumentalist free folk jam trio the Ghosts of Electricity. Mattingly recently completed his first year at Bard College, pursuing a double degree in music composition and classics.