Mullally and Coolidge join Steve Carell and Jennifer Garner, who will play the parents of Alexander (Ed Oxenbould).
Judith Viorst's 1972 children's book follows the title character throughout the course of one horrible day, thinking that bad things only happen to him. The live-action feature adaptation will be scripted by Rob Lieber.
Mullally has performed in Grease, How to Succeed in Business Without Really Trying and Young Frankenstein. Her TV credits include "Will and Grace," for which she received two Emmy Awards, "Parks and Recreation," "Happy Endings," "30 Rock" and "The New Adventures of Old Christine."
Coolidge has performed in The Women and Elling. Her film work includes "Legally Blonde," "American Pie" and "Austenland." Her TV credits include "The Secret Life of the American Teenager," "Frasier" and "Two Broke Girls."
Garner starred as Roxanne in Cyrano de Bergerac. Her TV work includes "Alias," and her film credits include "The Odd Life of Timothy Green," "Valentine's Day" and "Juno." Carell starred on "The Office," and his film work includes "Despicable Me," "Crazy Stupid Love" and "The 40 Year-Old Virgin."