M. Emmet Walsh, a paunchy and prolific character actor who was called “the poet of sleaze” by the critic Roger Ebert for his naturalistic portrayals of repellent lowlifes and miscreants, died on Tuesday in St. Albans, a small city in northern Vermont. He was 88.

His death, in a hospital, was announced by his manager, Sandy Joseph.

The most enduring praise Mr. Walsh received also came from Mr. Ebert: He coined the Stanton-Walsh Rule, which asserted that “no movie featuring either Harry Dean Stanton or M. Emmet Walsh in a supporting role can be altogether bad.”

In “Straight Time,” a 1978 film featuring both Mr. Stanton and Mr. Walsh, Mr. Walsh played a patronizing parole officer to Dustin Hoffman’s teetering ex-con. Mr. Walsh’s performance caught the eye of two brothers who aspired to be auteurs and were writing their first feature-film script.

The unknown Joel and Ethan Coen wrote the pivotal character of a detective in “Blood Simple” for Mr. Walsh. To their surprise, and despite offering little more in compensation than a per diem stipend, he accepted the role.

Reviewing “Blood Simple” for The New York Times in 1984, Janet Maslin said that Mr. Walsh had captured “a mischievousness that is perfect for the role.” Writing in Salon on the occasion of the release of Janus Films’ digital restoration in 2016, Andrew O’Hehir praised Mr. Walsh’s portrayal of a “sleazy, giggly and profoundly disturbing private detective.”