The actor will play Neil, a potential new roommate when Nick (Jake Johnson) considers moving in with Caroline (Mary Elizabeth Ellis), TV Guide reports.
Lennon will appear in the May 8 first season finale of the Zooey Deschanel show.
He is known for starring as Lieutenant Jim Dangle on Reno 911! from 2003 and 2009 and has had roles in Night at the Museum, Herbie Fully Loaded, Bad Teacher and What's Your Number?.
Lennon has also joined the ABC comedy Don't Trust the B**** in Apartment 23 with Bruce Davison.
Party Down star Martin Starr was cast as an old friend of Nick earlier this year.