Tandy's career covered stints with the St. George Illawarra Dragons, South Sydney Rabbitohs, Wests Tigers, Melbourne Storm, and the Canterbury-Bankstown Bulldogs in the NRL. He also played for the Hull Kingston Rovers in the Super League. In the National Leagues system he played for Doncaster, Widnes Vikings, Whitehaven and Barrow. He was an Ireland international. Tandy débuted for the Wests Tigers first grade team against the Brisbane Broncos in Round 15 2008. Tandy was selected in the Ireland national team for the 2008 Rugby League World Cup, which led to a contract with Melbourne Storm for 2009. He played for Melbourne in the 2009 NRL Grand Final victory against Parramatta, but the premiership title was later stripped from the Storm due to salary cap breaches. He signed with the Canterbury-Bankstown Bulldogs on 12 June 2010, and was sacked by them on 18 March 2011.
Betting scandal
After the 21 August 2010 Canterbury-Bankstown match against the North Queensland Cowboys Tandy became embroiled in a betting scandal. The Totalisator Agency Board announced that 95 per cent of bets placed on the first scoring play of this match were for the unusual option of a Cowboys penalty goal. Friends and associates of Tandy placed a large number of bets and then taken action in the match to allow the opposing side to score a penalty goal. Tandy gave away possession to the Cowboys in the opening moments of the match by knocking on, and then gave away a penalty. These actions put the Cowboys in a position where a penalty goal was a likely outcome. However, the Cowboys decided on an attacking option and scored a try instead. Tandy strongly denied the accusations of deliberately giving away possession and a penalty to allow the exotic option on the bets to be successful. Despite this, he was arrested on 2 February 2011 for providing false evidence to a law enforcement agency during the investigation of the betting scandal. He received an intensive correction order for six months. It required: community service, supervision and curfew, but he could have been jailed for two years. On 6 October 2011, Tandy was found to be guilty of manipulating the first scoring point of the game. He appealed the charge in January 2014 but lost the case. Tandy received a lifetime ban from NRL rugby league over the spot fixing.