Holmes, 31, will present the best featured actress award, alongside Harry Potter star and fellow Broadway veteran Daniel Radcliffe, at the 64th annual Tony Awards, to be broadcast live on CBS from Radio City Music Hall.
"Katie has proven herself a welcome addition to the Broadway community with her phenomenal debut last year in All My Sons and her continued support of theater," a Tony Awards source tells PEOPLE. "She and Daniel will bring a really great energy to the show this year, and everyone is really looking forward to working with her."
Radcliffe, 20, who played the troubled teen in the fall 2008 revival of the psychological drama Equus, is now set to star in next year's revival of the 1961 Pulitzer Prize-winning musical How to Succeed in Business Without Really Trying.
The nominees in the featured-actress category to be announced on Sunday by Holmes and Radcliffe are Maria Dizzia, in In the Next Room (or The Vibrator Play); Rosemary Harris, in The Royal Family; Jan Maxwell, in Lend Me a Tenor, and two actresses in another Arthur Miller revival, A View from the Bridge: Jessica Hecht and Scarlett Johansson.
This year's Tonys race is led by the musicals Fela! and the revival of La Cage aux Folles, with 11 nominations each. The revival of August Wilson's 1987 drama Fences, starring Denzel Washington, follows, with 10.