McManus played for the Knights in the Jersey Flegg Cup before graduating to their NSWRL Premier League team. He made is NRL début during the 2007 Newcastle Knights season. He was selected for Country in the City vs Country match on 8 May 2009. McManus got injured after playing one match for New South Wales rugby league team for the 2009 State of Origin series, therefore didn't take part in the rest of the series and resulting in McManus missing the second half of 2009 and the first half of 2010. On 13 March 2013, McManus re-signed with the Knights on a 3-year contract.