McGreal began his playing career with his local side Tranmere Rovers, where he progressed through the youth team to become a first-team regular, making over 200 appearances in nine years. He joined Ipswich Town in the summer of 1999, helping the club to play-off success and earning promotion to the Premier League in his first season. He spent five years with the Suffolk club, making over 150 appearances before joining Burnley in 2004. He ended his career in 2007 after making over 100 appearances for the club.
Born in Birkenhead, McGreal began his career with Tranmere Rovers, rising through the club's youth system to eventually become a first-team regular, making 195 league appearances between 1990 and 1999. He scored just one goal for the club in 233 appearances, with the opening goal on 23 February 1994 in a 1–1 draw with Leicester City at Filbert Street. Unfortunately for McGreal, his first goal was cancelled out when he scored an own goal when he sliced in Ian Ormondroyd's header which would otherwise have gone wide.
In the summer of 1999, with Huddersfield Town manager Steve Bruce and Ipswich Town manager George Burley both interested in signing McGreal, he opted to sign for the Suffolk club after a £650,000 offer was accepted by Tranmere.
McGreal made his Ipswich debut on 7 August 1999 in a 3–1 win over Nottingham Forest at Portman Road. He received his first red card in only his eighth match for the club on 11 September during a 1–1 draw with Portsmouth. He helped the team reach the play-off final at Wembley, where they beat Barnsley 4–2 to earn promotion to the Premier League.
In his third Premier League match for Ipswich, McGreal scored his first goal for the club with the opener in a 3–0 win over Everton at Goodison Park in a season which saw Ipswich climb the league table to ultimately finish fifth and earn a place in the 2001–02 UEFA Cup. He scored his second goal with the winner in a 2–1 win over Tottenham Hotspur on 12 January 2002, but he couldn't help halt the side's slide down the league as they finished 18th and were relegated back to the First Division.
The following season saw Ipswich once again playing in the UEFA Cup having qualified through the UEFA Respect Fair Play ranking, as McGreal scored in his first game of the new campaign as Town defeated Avenir Beggen 8–1 at Portman Road in the qualifying round second leg match on 29 August 2002. He scored once more in an injury-affected season with the opener in a 2–2 draw against Burnley, but could only muster 22 appearances all season. Another injury-hit season followed, where he missed much of the start of the season but returned to help Ipswich reach the play-offs, but they were defeated over two legs by West Ham United. McGreal scored once during the season in a 1–1 draw with Reading on 10 January 2004.
McGreal refused the offer of a new deal to remain with Ipswich in the summer of 2004 and instead opted to sign for Burnley on a three-year deal. Manager Steve Cotterill described McGreal as "one of the best defenders in the First Division". He made his debut for the side on 7 August 2004 in a 1–1 home draw with Sheffield United, before scoring what was to be his only goal for Burnley in a 3–0 win over Crewe Alexandra at Turf Moor on 11 September. He made 45 appearances in his first season, and a further 38 in his second, while he could only manage 23 first-team appearances during 2006–07 in a season again affected by injury.
After leaving Burnley at the end of the 2006–07 season, McGreal returned south, briefly joining Championship side Colchester United on trial, but manager Geraint Williams decided against offering the player a contract.
Following his release from Burnley and his trial with Colchester United, McGreal returned to the Ipswich area, and following advice from Town manager and his ex-teammate Jim Magilton, he studied for his UEFA B Licence.
After ex-Ipswich academy boss Tony Humes was appointed head of youth at Colchester United in 2009, McGreal joined the club's Academy as a professional development coach. He was later appointed manager of the under-18 side alongside his former Ipswich teammate Wayne Brown, and led the side to the Football League Youth Alliance South East title and won the Youth Alliance Cup in April 2014. Following Richard Hall's promotion to assistant manager in September 2014, McGreal stepped up to replace Hall as under-21s manager.
McGreal was named as interim manager at Colchester United alongside Richard Hall following Tony Humes dismissal as manager on 26 November 2015. However, following a 5–1 defeat against Burton Albion in his only match in charge, he was appointed assistant to Wayne Brown who was named caretaker manager on 2 December. Following Kevin Keen's appointment as permanent Colchester manager, McGreal reverted to his former role as under-21 coach.
After Kevin Keen left Colchester following the club's relegation to League Two on 26 April 2016, McGreal was appointed his successor on 4 May. He did not take charge of Colchester until after the final game of the season, in which his assistant Steve Ball was named caretaker. In his first match in charge on 6 August 2016, McGreal guided his side to a 1–1 opening day draw away to Hartlepool United. He earned his first win on 13 August as his side defeated Cambridge United 2–0 at the Colchester Community Stadium. After three wins and one draw in Colchester's opening five league fixtures, McGreal was nominated for the League Two 'Manager of the Month' award for August. After an eleven-game winless run, McGreal's side went undefeated in December, earning ten points from a possible twelve which propelled Colchester up the League Two table away from the relegation zone. In turn, McGreal was shortlisted for the League Two 'Manager of the Month' award for December. He won the award on 6 January 2017, becoming the first Colchester manager to win the award since Paul Lambert in January 2009.As of match played 16 September 2017.
2000 Football League First Division play-off final winner