Mumm attended The King's School, Sydney, along with fellow Waratahs Benn Robinson, Daniel Halangahu and Will Caldwell.

[2] Mumm graduated New South Wales Waratah Academy and went on to attend the University of Sydney where he played in SUFC sides which twice won the Tooheys New Cup.

[3] Although primarily a second-rower, Mumm has been utilised as flanker, making use of his athleticism whilst adding height to the line-out.

[8] In May 2013 Mumm was selected in a Barbarians line-up which faced England at Twickenham and the British and Irish Lions in Hong Kong.

[2] Greg is currently the managing director of The Final Whistle, a company that assists athletes with their life after sport career options.