He also at times covered for the likes of Dave Beasant, Hans Segers and Paul Heald, and also spent a period on loan at Crystal Palace.

It was during his tenure at Wimbledon that Sullivan was often acknowledged as one of the best goalkeepers in the league marked by his selection for the division's 1997–98 team of the season.

He helped Tottenham reach the 2002 Football League Cup Final which they lost to Blackburn Rovers.

[4] Chelsea began the 2003–04 season with three senior goalkeepers; Carlo Cudicini, Marco Ambrosio and Jurgen Macho.

Manager Dennis Wise told the press after Leeds' 2–1 victory against Coventry City that Sullivan had put on weight, and his performances were not as good, hence his loan to Doncaster.

[citation needed] Sullivan was also credited with a man-of-the-match performance against Aston Villa on 24 January 2009 which gave Doncaster a 0–0 draw that helped keep them in the FA Cup.

[18] The veteran goalkeeper continued to be an ever-present in the Rovers side throughout the 2009–10 season, appearing in all 46 league games for the club.

[citation needed] In 2010, Sullivan signed a one-year contract extension for Rovers, meaning he would be at the club until the end of the 2010–11 campaign.

[19] On 16 November 2012, Sullivan joined AFC Wimbledon on a short-term loan from Doncaster Rovers and made his debut the following day against Aldershot.

[citation needed] With first choice keeper Gary Woods injured, Doncaster recalled him for their game at AFC Bournemouth on 9 March 2013.

[21] Following his return to the Rovers' team from his loan spell in March 2013, Sullivan went on to play till the end of the season as Doncaster won the League One title and sealed automatic promotion to the Championship.

He was named in the Scottish squad for the 1998 FIFA World Cup in France, but was an unused substitute in all of Scotland's three matches.

[citation needed] Sullivan became the first choice Scotland goalkeeper after Jim Leighton retired from international football later in 1998, and he played regularly during the Euro 2000 and 2002 World Cup qualification groups.

[25][26] With an injury to Leeds substitute goalkeeper Jamie Ashdown, Sullivan revealed he had not officially retired from playing and would be willing to register himself as a player for the 2013/14 season.