Speaking to The Daily Telegraph, Whately explained that he has been surprised by the show's success.
"I was a bit of a naysayer," he said. "But it took off like a train so here we are back again."
Whately, who plays the title role, added that people enjoy the show's "familiarity", explaining: "People have always liked it, so they carry on watching it."
However, he also insisted that the episodes focus on the murder cases instead of on Lewis and his sidekick DS Hathaway (Laurence Fox).
"There is always a danger with a long-running series for it to disappear up its own arse, to become all about the regulars," he said. "Like hospital dramas where it's the main characters getting ill. Here I'm very aware that Lewis is the pivotal character, but the guests do all the acting."
Lewis returns on Sunday at 8.30pm on ITV1.