Hansard, 56, was the frontman for the Irish band The Frames, featured in the Irish film The Commitments, and won an Academy Award for best original song for 2007's Falling Slowly, which he co-wrote with Marketa Irglova for the movie Once.
In a statement to broadcaster RTE, his agents ATC management said: "With broken hearts we announce the passing of Glen Hansard who passed away, in the early hours of this morning, following a road traffic accident in Dublin.
"Glen's family is deeply shocked and heartbroken by this tragic loss and respectfully requests privacy at this extremely difficult time."
Irish prime minister Micheal Martin said Hansard was "a talented musician and actor who made a significant contribution to Ireland's cultural landscape over many years".
Hansard was one half of the rock duo The Swell Season, and released solo albums including Didn't He Ramble, which was nominated for a Grammy for Best Folk Album in 2016.
For years, he led the Christmas Eve charity busk outside The Gaiety Theatre in Dublin city, where members of the public gathered to see famous Irish musicians perform in aid of the Dublin Simon Community.
He also took part in protests against Ireland's housing crisis, a march to mark three years since Russia's invasion of Ukraine, and the anti-austerity water charge protests in 2014.
At the funeral of The Pogues frontman Shane MacGowan in 2023, Hansard performed Fairytale Of New York with Irish singer Lisa O'Neill, which prompted dancing in the aisles of the Co Tipperary church.
He is the father of a three-year-old boy, Christy.
Irish police said a man in his 50s died in single vehicle motorcycle crash in Lucan on the outskirts of the Irish capital early on Wednesday.
The man, who they did not name, was treated at the scene but was pronounced dead a short time later.
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