Mark Helias (born October 1, 1950) is an American jazz double bass player and composer born in New Brunswick, New Jersey.
He started playing the double bass at the age of 20, graduating from Yale University's School of Music with a Masters degree in 1976. He has also studied at Rutgers University. He teaches at Sarah Lawrence College, The New School, and SIM (School for Improvised Music).
Helias has performed with a wide variety of musicians, first and foremost with trombonist Ray Anderson, with whom he led the ironic 1980s avant-funk band Slickaphonics, and a trio with Gerry Hemingway on drums, formed in the late 1970s, later named BassDrumBone, and continuing to play together. Helias has also performed with members of Ornette Coleman's band, Don Cherry, Dewey Redman, and Ed Blackwell, and with musicians affiliated with the AACM, such as Anthony Braxton and Muhal Richard Abrams.
Since 1984 Mark Helias has released six recordings under his own name and further six albums leading the archetypal improvising trio Open Loose since 1996. The group comprises Helias on bass, first Ellery Eskelin, then Tony Malaby on tenor saxophone and Tom Rainey on drums.