McChrystal began his career at Wolverhampton Wanderers where he was one of a plethora of young players from Northern Ireland playing there. After spending three years at Molineux, including a spell on loan at Bradford City in 2003, he was released by the Midlands club and he eventually returned home to sign for his local team Derry City of the League of Ireland in April 2003, despite interest from other English clubs. He was then loaned out to near neighbours Institute by Dermot Keely on a three-month deal. His stay in the Irish League was short-lived however, and after just six games for the club, he picked up an injury in the quarter-final of the North-West Cup against Moyola Park which hastened his return to Derry City. He fought his way back into the team under Gavin Dykes and Peter Hutton but did not appear regularly during the reign of Stephen Kenny due to stiff competition in defence. Seen to be surplus to demands, he was released on 14 December 2006 after the appointment of Pat Fenlon as manager. Within a month he had moved to Glasgow-based club, Partick Thistle. He made his Jags debut in a 2–0 defeat by Clyde on 2 January 2007 and was a regular through to the end of the season. He scored his only goal in a 4–3 defeat by Queen of the South as Partick almost came back from 4–0 down. He re-signed for Derry City in August 2007 after turning down a move to Glentoran and being released by new Thistle manager Ian McCall. The following year he collected his first major honours, a winner's medal in the League Cup as Wexford Youths were routed 6–1 and a runners-up medal following an FAI Cup Finalpenalty shoot-out defeat by Bohemians. Unhappy with his limited first team chances after returning from a broken cheekbone and non-payment of wages, he negotiated an early release from his Derry contract in August 2009. He went on trial at Huddersfield but failed to win a deal and Crewe Alexandra before joining Lisburn Distillery on a short-term deal in late 2009. Unhappy over non-payment of his wages by Lisburn he rejoined Derry City for a third spell in January 2010, signing a one-year contract. He then went on to help Derry back into the Premier Division as First Division Champions. On 6 January 2011 he joined English club Tranmere Rovers on a six-month contract and made his Football League debut as a 77th-minute substitute on 8 January against Walsall. At the end of the 2010–11 season he offered a new contract by the club and at the end of June he signed a two-year contract. His first goal for the club came against Scunthorpe on 5 May 2012 in Tranmere's final match of the season. On 3 January 2013, he signed a short-term contract with League Two side Bristol Rovers. He made his home debut on 5 January in a 2–0 defeat to Gillingham. On 10 March 2017, it was confirmed that McCrystal had left the club after 4 years. He signed for Crusaders on 18 July 2017. Derry City announced on 4 July 2019, that they had signed McChrystal on a 1-year contract.
International career
He gained Schoolboy caps while at St. Columb's College in his native Derry, and added Under-18 caps whilst at Wolves. He appeared nine times for Northern Ireland's Under 21 team, making his debut on 18 August 2004 against Switzerland, with his last appearance coming almost two years later on 16 August 2006 against Romania.
Personal life
He holds a degree in Business Studies with Accounts.
