Butler, 58, has been the Steelers' linebackers coach since 2003 and has been viewed as the team's DC in waiting.
The legendary LeBeau announced his resignation from the Steelers over the weekend after 13 seasons, though he said he's not retiring.
Butler spent 10 seasons as an NFL linebacker with the Seattle Seahawks from 1978-1987 after being drafted No. 36 overall.
The elevation to defensive coordinator duties is no surprise as the Steelers have blocked teams who've requested to interview Butler for positions the past several years.
Butler takes over a defense that could see a shape-shift this offseason, with the future of veterans Troy Polamalu and Ike Taylor -- among others -- in question.
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