The 2000 AD editor is thought to be replacing Grant Morrison on the Superman title when his run comes to an end with issue #16.
Bleeding Cool unearthed the rumour, which intensified following a Twitter post from Diggle. "So I just landed the biggest job of my career. Terrified," he wrote.
Diggle garnered critical acclaim for his recent run on Marvel Comics' Daredevil. He has since worked on Six Guns for the publisher, and penned issues of Doctor Who for IDW Publishing.
Morrison previously announced that he is moving away from the superhero genre, with his run on Batman Incorporated coming to an end on #12.
DC Comics is expected to announce Diggle's appointment as Action Comics writer at the New York Comic Con in October.