The "Star Wars" actor, whose great-grandmother was born in Ireland, was invited to represent the Irish diaspora at the celebration. Hamill spent time on Ireland's rocky Skellig Michael island filming the most recent "Star Wars" movie, "The Last Jedi."
Hamill sported a tweed cap, a green scarf and a shamrock sprig as he attended the parade, which sees floats, colorfully clad performers and marching bands wind their way through the Irish capital.
"Game of Thrones" actor Liam Cunningham was the grand marshal of Saturday's parade, attended by Irish President Michael D. Higgins.
Irish Prime Minister Leo Varadkar is at New York's St. Patrick's Day parade.