Born 29 March 1974 in Guisborough, Gregan built a reputation as a tough-tackling, no-nonsense defensive-midfielder and occasional centre-back. Starting his professional career at Darlington, he made over 130 league appearances between 1991 and 1996, before moving to Preston North End in November 1996 for £350,000. At Preston, he was converted from defender to central midfielder, becoming team captain in December 1997, earning two successive PFA Second Division Team of the Year nods, and tallying over 200 league games and 12 goals by 2002.

In August 2002, Gregan signed for West Bromwich Albion, newly promoted to the Premier League for £2 million, quickly becoming a fans' favourite. Playing 36 league games and scoring once, he could not keep the Baggies up. The following season he helped lead West Brom to promotion, finishing runners-up in Division One with 43 appearances and another goal, solidifying his leadership credentials.

In September 2004, then-Leeds manager Kevin Blackwell recruited Gregan for an initial £500,000 rising to £1 million depending on appearances and promotion, seeking experience and leadership to steady Leeds after their relegation from the Premier League. Gregan signed a three-year deal and quickly established himself in midfield or at centre-back depending on team needs.

Gregan made 35 league appearances in his first season (2004/05) and featured once as substitute, without scoring any goals. Despite Leeds finishing mid-table, he was praised for his improvement and strong performances. Neil Sullivan, the club's Player of the Year that season, singled Gregan out for admiration, noting how he had won over fans despite early scepticism and became a key part of Leeds' rebuilding process.

Gregan's professionalism stood out amid a season of transition and turmoil. He addressed developing youth and younger team-mates with consistency, and even when results wavered, his attitude remained commended by both staff and supporters. He admitted the season had been one of frustration carried over years, but felt players like himself, Michael Gray, and Paul Butler helped steady the dressing room with experience.

In the 2005/06 season, Gregan featured 28 league games as Leeds reached the Championship playoff final. His positional awareness, aerial dominance, and tackling were considered vital to Leeds' push for promotion.

Gregan faced his share of criticism, too — including a worrying incident where he and his young family were verbally abused by a small section of fans after a poor result to Leicester in December 2004, prompting the club to launch an investigation over the unacceptable behaviour. Still, many recognised his professionalism in the face of abuse and the difficult transition the club was going through.

By early 2006/07, Leeds had undergone a full squad and managerial overhaul under new coach Dennis Wise. Gregan found himself out of first-team plans amid the emergence of younger defenders like Matthew Kilgallon and Frazer Richardson. He managed just one league appearance and one League Cup outing in that season before being loaned to Oldham Athletic in November 2006 - a move that became permanent in January 2007.

Gregan's departure marked the end of a chapter that saw him transition from Preston captain to Leeds' middle-division workhorse, in a period marked by financial instability, relegation aftermath, and shifting styles of play.

Gregan captained Oldham through successive League One campaigns, making over 120 league appearances and chipping in with a goal from midfield, while also guiding them to play-off campaigns and cup runs between 2007 and 2010. Late in his career he spent time at Fleetwood Town before retiring in 2011.