After leaving Dunfermline at the end of the 2014–15 season, Millen signed for Scottish Championship side Livingston in July 2015. Millen stayed with the side for only six months, leaving in January 2016 in order to seek regular first-team football. Shortly after leaving Livingston, Millen signed a six-month contract with Clyde who he previously played for as a youth player. At the end of his contract, Millen was released by the Cumbernauld side. At the beginning of July 2016, Millen was signed by Scottish League Two side Queen's Park, with whom his father Andy Millen finished his playing career with.
