Nealy, whose Broadway credits include the original and 1987 revival productions of Dreamgirls, will play the role of Jimmy.
Performances at the St. Louis venue are scheduled for July 16-22.
The cast will also feature the previously reported Demetria McKinney as Deena, Jenelle Lynn Randall as Lorrell, Muny veteran Ken Page as Marty, Christopher Jackson as Curtis, Karla Mosely as Michelle and Tommar Wilson as C.C.
The production will be directed by Robert Clater with choreography by Lesia Kaye.
Executive producer Mike Isaacson added, "The Muny audience will be astounded by the talent of Jennifer Holliday. The explosive power of her voice on the Muny stage is a fitting tribute to the 30th anniversary of this landmark musical and the Muny’s tradition of iconic musical theatre under the stars.”
A native of Houston, Jennifer Holliday made her professional New York theatre debut in 1980 in the revival of Your Arms Too Short to Box With God. That role led to her Tony-winning performance in Dreamgirls, and her rendition of that show's "And I Am Telling You I'm Not Going" earned the singer-actress her first Grammy Award. She has also appeared on Broadway in the revivals of Grease! and Chicago, and her television credits include "Ellen," "Touched By an Angel" and a recurring role on "Ally McBeal." Holliday earned another Grammy Award for her recording of Duke Ellington's "Come Sunday."
Dreamgirls debuted on Broadway at the Imperial Theatre in December 1981. The musical, directed by Michael Bennett, earned 11 Tony Award nominations in 1982 and took home six, including Best Book, Best Choreography, Best Lighting and a host of acting honors.
For more information visit www.muny.org.