The 21 Jump Street star will play an uptight single mother in the pilot, Deadline reports.
The character needs help to raise her young daughter and moves in with her laid-back brother (Nat Faxon).
Saturday Night Live's Abby Elliott was originally cast in the role, but later dropped out of the project following the first table read.
Johnson's credits include 2010 film The Social Network and forthcoming Jason Segel comedy The Five-Year Engagement.
The Ned Fox pilot is loosely based on the life of writer Dana Fox (Couples Retreat, What Happens in Vegas).
Other comedy pilot pick-ups at Fox include the basketball-themed sitcom Rebounding and Let It Go starring Chuck's Zachary Levi.
> TV's Best New Show Pilots for 2012