The crime thriller stars Doctor Who actors David Tennant and Arthur Darvill, as well as Olivia Colman (Tyrannosaur) and Vicky McClure (This Is England).
Mellor told Digital Spy that he is "really excited" to be a part of the eight-part series, which he described as "the biggest drama I've ever done".
"I don't want to give anything away about my character, but all I can say is, it's the most different character I've ever played," he hinted. "I will look and be a lot different than how you're used to seeing me."
Mellor - who stars in BBC sitcom In with the Flynns - added that he is keen to balance comedy and drama in his career.
"I'm really grateful that ITV have given me another chance to do a drama," the 36-year-old said. "It means that I don't get stuck in the pigeonhole of being a comedy actor."
The second series of Will Mellor's BBC One comedy In with the Flynns begins on Friday, August 17 at 9.30pm on BBC One.
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