Alfred A. Knopf has fired a longtime editor who worked with such literary stars as Raymond Carver, Annie Dillard and Cormac McCarthy in what it called a breach of company policy.

On Friday, a spokesman for the New York-based publisher confirmed that the editor, Gary Fisketjon, had been suspended and then dismissed after an investigation, though he declined to specify details of the policy breach. Mr. Fisketjon’s firing was reported earlier by Publishers Lunch, a publishing industry website.

Mr. Fisketjon, an editor at large and vice president at Knopf, did not immediately respond to email and phone messages seeking comment.

In a career spanning around four decades, Mr. Fisketjon helped to shape contemporary American literature. Tobias Wolff, Patricia Highsmith, Donna Tartt, Haruki Murakami, Bret Easton Ellis, Richard Russo, Kent Haruf and Julian Barnes are among the authors whose work he discovered and elevated.