He made his Millwall debut on 6 August 2013 in the first round of the League Cup in a 2–1 home win against AFC Wimbledon. Bywater played in Millwall's next three league games, against Ipswich Town, Huddersfield Town and Sheffield Wednesday and a 2–1 defeat by Nottingham Forest in the second round of the League Cup. Regular goalkeeper, David Forde resumed in the goalkeeper position for Millwall until January 2014. On 18 January 2014 Bywater replaced Forde at half-time in a 1–0 home win against Ipswich Town, a match which saw new Millwall manager, Ian Holloway's first win a manager of the club.