McChrystal began his career at
Wolverhampton Wanderers he was released by the
Midlands club. McChrystal eventually returned home to sign for his local team
Derry City of the
League of Ireland in April 2003, 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 Final penalty 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 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.
Bristol Rovers On 3 January 2013, he signed a short-term contract with
League Two side
Bristol Rovers. He made his home debut on 5 January as bottom-club Rovers were defeated 2–0 by league leaders
Gillingham. On 30 April 2013, McChrystal signed a new two-year contract with the club. On 4 September 2013, McChrystal scored his first, and what to be proved only, goal for the club with an equaliser as Rovers were defeated 2–1 by arch rivals
Bristol City in the
Football League Trophy First Round, the first meeting between the two in six years. McChrystal featured in the final match of the season as Rovers lost 1–0 at home to
Mansfield Town, condemning the club to relegation from the Football League for the first time in the club's history. McChrystal was appointed captain by manager
Darrell Clarke for Rovers' maiden season in the
National League. On 2 December 2014, after goalkeeper
Steve Mildenhall was forced off with a knee injury in the 42nd minute of the match, and without a recognised goalkeeper on the bench, McChrystal went in goal, keeping a clean sheet as Rovers earned a 0–0 draw away at
Wrexham. The season ended in success for Rovers as they returned to the Football League at the first time of asking, the first club to do so since 2005, defeating
Grimsby Town 5–3 on penalties at
Wembley after the club finished second in the regulation season. Following their promotion back to League Two, McChrystal found first-team opportunities hard to come by at times with the defender making only ten appearances before February 2016. He featured heavily in the run-in however as Rovers gained momentum before a 92nd-minute winner from
Lee Brown against
Dagenham & Redbridge on the final day of the season saw Rovers sneak into the final automatic promotion place, confirming back-to-back promotions for the club. Following promotion, McChrystal signed a new contract with the club. On 10 March 2017, it was confirmed that McCrystal had left the club after 4 years.
Return to Ireland and coaching career McChrystal signed for Crusaders on 18 July 2017.
Derry City announced on 4 July 2019, that they had signed McChrystal on a 1-year contract. In February 2021, McChrystal was appointed player-coach at Derry City, combining this role with the role of Under-13 Coach. McChrystal stayed on at the club as a first-team coach following his retirement. In December 2022, he assumed a new role as Professional Development Coach. ==International career==