Kimmel shared the happy news with Ellen DeGeneres during taping of an Ellen episode to air Wednesday.
"I’m having a baby," Kimmel said. "Wait I want to finish -- with Ellen," he joked.
"Let’s take that in because they don’t know if you’re serious or not. You and Molly are having a baby and that’s very exciting," DeGeneres clarified.
Kimmel married McNearney, a co-head writer on his show, in a star-studded ceremony last year.
"I have a 20-year-old son and a 22-year-old-daughter and I’ve really forgotten everything," he continued. "There are new ways to do things. You hold them by the front of the neck now it seems."
“I told my daughter, ‘Listen, there’s only so much love I have to give. You’re gonna have to split it up with the new kid. There’s a finite amount of love and that’s that.’ So they’re dealing with it, but it is very weird at my age. I’m going to be one of those old dads," he said.