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.
The best of London's West End theater scene is honored at the annual ceremony.
The musical features the Academy Award-winning music and lyrics of Glen Hansard and Markéta Irglová.