His most memorable movie roles include boorish hick bartender Dan Oldum in Jackson County Jail, hard-nosed detective Sergeant Cook in Night Warning, cranky toy store manager Mr. Sims in Silent Night, Deadly Night, trailer park resident Mr. Potter in The Last Starfighter, Anthony Michael Hall's plumber father in Weird Science and redneck hunter Reg in The Great Outdoors.
During the fall of 1976, Leach was cast in the role of Mickey "Wig" Wiggins, an airplane mechanic, in the eleven-episode CBS adventure series Spencer's Pilots, starring Gene Evans, Christopher Stone and Todd Susman.
Among the many television shows on which he has appeared are The Brady Bunch, The Partridge Family, Insight, Bonanza, Hawkins, Three's Company, Tales from the Crypt, and Newhart.
From 1992 to 1999, Leach was co-editor and publisher of Country Connections, an award-winning bi-monthly magazine which covered environmental and progressive social issues.
In 2007, Leach did not renew his membership in the Academy of Motion Picture Arts and Sciences and wrote of his frustration with DVD screeners in a satirical piece on his website.