No word yet on who will play the show's three other lead characters - Sky Masterson, Sarah Brown and Miss Adelaide. The show's last Broadway revival of the musical, in 1992, featured a cast that included Nathan Lane and Faith Prince.
Platt made his Broadway debut in 2006 in Conor McPherson's "Shining City," for which he received a best-actor Tony nomination. He has appeared in such TV series as "Huff" and "The West Wing," and will be seen in the film version of "Frost/Nixon."
"Guys and Dolls" will be directed by Des McAnuff and feature choreography by Sergio Trujillo.
McAnuff, artistic director of Canada's Stratford Shakespeare Festival, worked with Trujillo on the current Broadway success, "Jersey Boys."
"Guys and Dolls," which has a score by Loesser and a book by Jo Swerling and Abe Burrows, originally opened on Broadway in 1950.