As a player, Whitlow was primarily used as left-back. He began his professional career at Leeds United, whom he joined from non-league Witton Albion in November 1988. He spent four seasons at Leeds and played slightly below 100 games for the team. In March 1992 Whitlow was sold to Leicester City for a £250,000 transfer fee. Leeds went on to win the old First Division a few months later which Whitlow had contributed to with ten league appearances and a goal against rivals Sheffield Wednesday. Despite making enough appearances to earn a medal, he did not receive one at the time as he already left for Leicester by the time Leeds had been confirmed as champions. However, 10 years on he received a letter from the Professional Footballers' Association informing him that he would belatedly receive the medal he was entitled to.
At Leicester Whitlow became a first-team regular and was a member of the side that won the 1997 League Cup. In total he played 180 games for the Foxes and scored nine goals. He then moved on to Bolton Wanderers in September 1997 for a £500,000 fee. At Bolton Whitlow is remembered for being sent off in the dramatic 2000 playoff semi-final against Ipswich Town that Ipswich went on to win 5-3 after extra time following a Jim Magilton equaliser in the last minute of normal time. The following season Whitlow missed most of the action because of injury but he returned to the side just in time for the playoffs where Bolton this time got promoted to the Premier League.
After six seasons at Bolton with 163 first-team appearances to his name Whitlow was released at the end of the 2002-03 season. He spent the 2003-04 season at Sheffield United scoring once against Burnley and then joined Notts County the following season as player-coach. His last competitive match for County came in March 2005 although he remained registered as a player at the club until 2007.
Marshall made his name playing as a defender and striker for Oldham Athletic but started his career as an apprentice with hometown club Everton. After four years he signed for Oldham for £200,000 and scored nearly 50 goals in almost 200 appearances before joining Ipswich Town in 1993 for £750,000.
At Portman Road he scored 38 times in just over 90 appearances, including five times in his first five games, a feat that has not been repeated since in the Premier League, before being sold to Leicester City for £800,000 in 1996. He played for the Foxes for four seasons, notching up 26 goals in 61 games. He left on a free transfer to Bolton. While at Leicester, Marshall was part of the 2000 League Cup winning team, coming on as a substitute in the final. In April 1999 he also scored a memorable last minute winner against boyhood club Liverpool at Anfield.
After helping the Wanderers to the Premier League, he went on loan to Blackpool before making the move to Bloomfield Road permanent in January 2002. He scored once for Blackpool, in a 2-1 defeat to Huddersfield Town in February 2002. He captained the side for their victory in the final of the LDV Vans Trophy at the Millennium Stadium on 12 March 2002. "I was carrying an injury and wasn't 100% fit, but I had decided to call it a day and I wanted to finish on a high, which I did. It was a great day, and night come to think of it, and it will be one I will never forget."
During his career he has enjoyed spells at Leicester City, Stoke City, Bolton Wanderers, IA Akranes, Nürnberg, Feyenoord and Dundee United.
As a young player, Gunnlaugsson made several appearances for the Icelandic international youth teams. Arnar made his debut for Iceland in an April 1993 friendly match against the United States. He went on to earn 32 caps, scoring three goals between 1993 and 2003. His last international match was in April 2003 and a friendly match against Finland in which he was substituted.
Others who have played for both sides include - Frank Worthington, Stevie Howie, Les Ferdinand, Steve Whitworth, Jermaine Beckford, Neil Danns, Franz Carr, Mark Davies, Trevor Hebbard, Russel Hoult, Bruno N'Gotty, Peter Shilton, Gerry Taggart, Steve Thompson and Gavin Ward.