Actor Stuart Townsend will take time out from Hollywood this weekend to protest against the routing of the M3 motorway near the Hill of Tara, campaigners said.
Townsend is expected to join demonstrators at the Dáil on Saturday.
Hothouse Flowers singer Liam O'Maonlaí will also turn out in Dublin in a show of opposition to what protesters say is the destruction of parts of the archaeologically rich Tara valley.
Harpists will play outside Leinster House, in a symbolic gesture of Irish heritage, as a petition to Minister for Environment John Gormley demanding an alternative to the current plans is handed over.
Townsend (36), from Howth, in north Co Dublin, is to join his friend aerial photographer John Quigley on Sunday for another demonstration at the Hill of Tara.
The pair are to fly over the ancient Co Meath landmark to take photographs of hundreds of campaigners forming a "human harp".
Other harpist events are to take place outside Irish consulates in New York, Chicago, and Los Angeles at the same time as the Dublin protest, according to protesters.