The veteran musical leads the charge of Broadway productions taking their final bows this weekend.
After nearly four years, the pair says goodbye to onstage bars, broken guitars, and Raglan Road.
Paul Nolan and Jessie Fisher will take part in the evening at the Hammerstein Ballroom.
Irglová won an Oscar for her song "Falling Slowly," from the film version of the Tony-winning musical.
The Broadway casts of Wicked and Once have joined the star-studded lineup of performers.
Watch a bunch of Broadway stars dump freezing-cold water on themselves.
The Oscar winner joined the cast onstage to sing a special encore finale.
The casts of A Gentleman's Guide to Love & Murder and iLuminate were also on hand for the weekly outdoor concert.
The Tony-winning production's "Girl" offers an inside look on the differences between standing by and leading the show nightly.