Guy started his career with his home-town club Leicester City. The central defender went out on loan to several clubs in order to gain first team experience, and Diamonds were the first club to take on the young defender. He signed in October 1997, initially for one month, but this was extended to three months. He made 12 appearances before returning to Leicester. He had further loan spells with Colchester United and Plymouth Argyle, before returning to Nene Park in March 1999. until the end of the season. Guy made an additional 10 appearances before returning to Leicester once more.

At the start of the 1999/2000 season, he went on loan to Lincoln City before a loan spell with Rotherham United in October 1999 which eventually led to a permanent move the following month when the Millers paid a £50,000 transfer fee. He made over 100 appearances, before loan spells with Wycombe Wanderers and Peterborough United, followed by a free transfer to Sheffield Wednesday in June 2004. A further loan period at Peterborough United followed, before a short term deal at Oldham Athletic and a permanent move to Peterborough in July 2006. There were loan deals at Rochdale (August 2007) and Northampton Town (November 2007), before he was released in January 2008. He joined Notts County on a short term deal before signing for Kettering Town in February 2008. A move to Burton Albion followed in the summer of 2009, but he found himself on loan again in January 2010 when he went to Torquay United - the move being made permanent on 21 July 2010 when he signed a one year deal. He left the Gulls at the end of the season, and joined League Two side Bradford City on 13 June 2011. He made 13 appearances for the Bantams, but went on a three month loan deal to Rotherham United on 14 October 2011, receiving a red card in his first game back with the Millers on the same evening.