A wide-sided forward, Donnelly started his career at Queen's Park but left in 1993 to join Celtic. He made his league debut towards the end of the 1993–94 season, appearing as a substitute in a 0–0 draw against Hibernian. Playing in the majority of matches from March onwards, Donnelly netted five league goals in 12 appearances. He failed to improve on this tally in the following season as he did not score in 17 outings, although the team reached both domestic cup finals, and he was part of Celtic's Scottish Cup-winning side. In the 1995–96 season, Donnelly became a regular, missing only one league match and scoring six goals, and featured in the majority of the 1996–97 campaign. The 1997–98 season saw Donnelly's best return of goals, scoring 10 goals in 30 league matches as Celtic won the Scottish Premier Division and Scottish League Cup. The following season, he netted five goals in 23 appearances in what was his final year at Celtic Park. In July 1999, Donnelly – along with Phil O'Donnell – joined Sheffield Wednesday on a Bosman free transfer. Donnelly's time at Wednesday was interrupted by a series of injuries and he played only a dozen matches in the Premier League that season, scoring once as Wednesday were relegated. The following season, he featured in just three matches, although he played in 23 games in the 2001–02 season. In his final season at Hillsborough, Donnelly scored two goals in fifteen league matches before being released. Joining Coventry City on trial, Donnelly instead returned to Scotland with St Johnstone, signing a one-year deal in August 2003. Surprisingly, given his injury history, he featured in every league match of that season, scoring eight goals before signing for Dunfermline Athletic in July. During his time at East End Park, his injuries returned and he was released two years later having made fewer than forty league appearances. He joined Partick Thistle in June 2006 and played regularly for three seasons. He was initially released at the end of the 2008–09 season, and made a substitute appearance for Greenock Morton in a friendly against Oxford United. However, following the departure of Partick coach John Henry to Burnley, Donnelly rejoined the Jags as a player-coach, scoring against Morton in a 2–0 win at Cappielow later that season. In a similar pattern, Donnelly was then released by Partick again at the end of the 2009–10 season, but soon re-signed once more on a one-year contract. In 2011 he ceased playing but continued at the club as a coach after his friend and teammate Jackie McNamara was appointed manager.
International career
At end of the 1996–97 season, Donnelly made his Scotland debut, making substitute appearances in the friendly matches against Wales and Malta. The following season Donnelly also featured regularly for Scotland, playing in a number of friendlies ahead of the 1998 World Cup, although he failed to make an appearance during the tournament. Donnelly won ten Scotland caps during his career, and had played for Scotland under-21 before appearing for the senior side.
Coaching career
On 30 January 2013, Donnelly left Partick Thistle and joined Dundee United as assistant manager, accompanying Jackie McNamara who had been appointed manager. He left Dundee United in September 2015, following McNamara's departure. Donnelly was announced as York City's assistant manager two months later, following McNamara to Bootham Crescent. After McNamara's resignation as manager and appointment as chief executive, Donnelly left the club on 16 October 2016.
