At the age of 19, while at Northwestern, he received his first award for directing a production of Tennessee Williams' Cat on a Hot Tin Roof.

[7] He then directed Wilson's The Sand Castle or There is a Tavern in the Town or Harry Can Dance[8] and The Girl on the BBC,[9] both at La MaMa in 1965.

[10] That same year, Mason directed a production of Donald Julian's A Coffee Ground Among the Tea Leaves at La MaMa.

[12] Since their early collaboration at La MaMa, Mason has directed over sixty productions of Lanford Wilson's plays.

Among these productions are The Hot l Baltimore, for which Mason won his first Obie Award for Distinguished Direction in 1973; Fifth of July (1978); Talley's Folly (1979); Angels Fall (1983); Burn This (1987); and Redwood Curtain (1992).

On television, Mason has directed William Inge’s Picnic, Lanford Wilson’s The Mound Builders and Fifth of July, and Robert Patrick’s Kennedy's Children.

[29] He wrote Creating Life On Stage: A Director's Approach to Working with Actors (2007) and The Transcendent Years: Circle Repertory Theater and the '60s, published as a Kindle e-book in 2016.

On July 25, 2011, the first Monday after New York State enacted its marriage equality law, Mason married his partner of 37 years, theater artist Daniel Irvine.