Newcastle-born Mark having come through the United YTS ranks before initially signing a one year deal in the summer of 2010, shortly after becoming the youngest ever goalkeeper to appear in the Cumbrians first team. Gillespie, at 18 years and 42 days old, coming on as a stoppage time substitute for Adam Collin in a 2-0 victory at Norwich on the final day of the 2009-10 League One campaign.
Collin remaining injury and suspension free though has meant Gillespie is still waiting for his second game in a Carlisle shirt, Collin having now made 132 starts in a row for Carlisle, since Lenny Pidgeley kept goal at Leeds in the Johnstone's Paint Trophy on the 19th January of 2010. Gillespie also only able to spend three months kicking his heels out on loan, at Blyth Spartans in late 2010/early 2011.
Highly rated by the United coaching staff though Mark signed a further one year deal in the summer of 2011, before being an unused substitute in a hefty 42 games for the Blues last season. Performances in training and reserve friendlies have still been good however and Carlisle have rewarded their faith in the 20-year old by giving him a two-year contract this time around, with next season presumably seeing a plan in place to send Mark out on loan for a period of time.