Having begun his career as a trainee with Wimbledon, Martin signed for Manchester United as a 16-year-old in 2003.
He made his debut for Sir Alex Ferguson’s side in their League Cup victory against Barnet in October 2005, before joining United’s feeder club Royal Antwerp on loan in January 2006. His five-month spell in Belgium was a success; he earned the team’s Fans’ Player of the Year award and was voted Man of the Match in five-consecutive games.
Following a loan spell with Rangers (August to December 2006), the attacking midfielder gained invaluable Championship experience with Stoke City (January to May 2007), Plymouth Argyle (October 2007 to January 2008), Sheffield United (January to May 2008), and Nottingham Forest (August to November 2008).
Martin made his only Premier League appearance for United on the final day of the 2008/09 season, playing the full 90 minutes in a 1-0 victory over Hull City.
Former United midfielder Roy Keane paid a reported fee of £1.5m to take Martin to Ipswich Town in July 2009. He scored within eight minutes of his first start of the Suffolk club, a 3-1 pre-season friendly victory over Brentford.
The Taunton-born player made 89 starts across all competitions during his four years at Portman Road, a period that also featured a successful half-season loan at Charlton at the start of the 2010/11 campaign.
Following his release, he signed a one-year contract with Millwall in July 2013, and his performances during his maiden season with the London club earned him a two-year extension the following summer. Martin played 29 times in his first two seasons at The Den, but found opportunities limited during the 2015/16 campaign.
His last competitive action prior to joining the Gills on a free transfer in July 2016 was a 10-game loan spell with eventual League Two champions Northampton Town.