Cillian O'Sullivan (born 1989 or 1990)[1] is an American-born Irish actor who has had roles in Then You Run (Sky 2023),[2] In From the Cold (Netflix 2022),[3] Bull (CBS 2019),[4] Vikings (History 2016),[5] 6Degrees (BBC 2012),[6] Single-Handed (RTÉ 2009),[7] and Seacht (BBC/TG4 2008).
[8] Born in New York to Irish parents,[1] O'Sullivan's family moved back to Ireland when he was a child, and he attended school in Ballinlough, Cork.
[5][9] Misty Button, in which he had a lead role,[10] won the "best narrative feature" at the 2019 San Luis Obispo International Film Festival.
[11] In 2021, he filmed a Sky Studios series titled Then You Run,[9][12] which was released in July 2023.
[13] In mid-2024, he was included in the cast of the proposed third season of Star Trek: Strange New Worlds.