Gwilt's mother is from Papua New Guinea[1] and his father, Jason, is of Welsh descent and immigrated with his parents and siblings from Crowle (Worcestershire) in England to Australia in the late 1950s.

[4] He made his debut in the final round of the 2005 AFL season, against the Brisbane Lions at Telstra Dome, in a match where the Saints won by a club-record 139 points and small forward Stephen Milne kicked eleven goals.

He enjoyed better form after being played as a forward, including a good performance in St Kilda's 2008 semifinal win against Collingwood.

Gwilt played in 15 of 22 matches in the 2009 season home and away rounds in which St Kilda qualified in first position for the finals, winning the club’s third minor premiership.

[9] Gwilt played 26 games in 2010, including four final matches, and finished 8th in St Kilda's best & fairest award (Trevor Barker Medal).