Wetherall, who made his Broadway debut in the title role of The Elephant Man, will appear as Willie, opposite Ivey (Butley, Heartbreak House), who was previously announced to star as the chattering Winnie.
Westport artistic director Mark Lamos will direct Beckett's post-apocalyptic two-hander that will run July 6-24.
The existential comedy centers on Winnie, buried above her waist in a mound of blasted ground in a barren, sunburnt landscape. With only a mysterious bell to measure the passing of time, Winnie talks away (and occasionally to her wandering husband) as she rifles through the items in her purse and muses on life.
Happy Days will have scenic and costume design by John Arnone, lighting design by Stephen Strawbridge and sound design by John Gromada.
Wetherall appeared Off-Broadway in The Glass Cage, Pride's Crossing, Henry VI and Tamara. His screen roles include "Queer as Folk," "Spider-Man 2" and "Guiding Light." Dana Ivey earned Tony nominations for her performances in Butley, Heartbreak House, Sunday in the Park with George, The Last Night of Ballyhoo and The Rivals and won Drama Desk Awards for The Last Night of Ballyhoo and Sex and Longing. She appeared in the original Off-Broadway staging of Driving Miss Daisy and in The Savannah Disputation at Playwrights Horizons last season.