Welsh "B" international Mark Walton began his career at his local league club Swansea, being a native of Merthyr Tydfil. He joined Luton in February 1987 but failed to make the first team. He joined Colchester in August 1987 and made 40 league appearances before transferring to Norwich for £75,000 on the recommendation of his former manager Mike Walker.

Mark spent 1989 to 1992 at Carrow Road. Primarily the understudy to Bryan Gunn, Mark was a member of the Norwich side that reached the semi-finals of the FA Cup in April 1992 when Gunn was injured. He made 28 appearances for the first team and 114 for the reserves.

A lack of first team opportunities saw Mark request a transfer in April 1993. Loan spells with Wrexham and Dundee United followed. By Febraury 1994 he was on a monthly contract and seeking trials with a number of sides including St Johnstone and West Ham. He joined Bruce Rioch's Bolton Wanderers in March 1994 playing three games for the Trotters.

Without a club in the summer of 1994, he spent the next two years in non-league football in both Norfolk (Wroxham (September 1994) and Fakenham(Juky 1996)) and South Wales (Merthyr Tydfil (Nov 1994) and Barry Town (June 1995))

Mark joined Fulham in 1996, he was first choice keeper in the side that came second in Division Three (1996-97). However Mohamed Al Fayed and Kevin Keegan's revolution at Craven Cottage resulted in the signing of South African international goalkeeper Arendse and former Southampton keeper Maik Taylor. Dropping down the pecking order in Fulham's team of superstars, Mark joined Gillingham on loan in February 1998. An inability to agree personal terms with the Gills curtailed a £30,000 move to Kent. Mark was also linked by Yahoo's Teamtalk service with a move to Brentford but he chose to see out his time at Craven Cottage in the knowledge that South African keeper Arendse was unlikely to have his work permit renewed.

Norwich manager Mike Walker surprised everyone on Transfer Deadline Day (26th March 1998) when he brought Mark back to Carrow Road on loan to provide cover for Andy Marshall following Bryan Gunn's recent departure.

At the start of July 1998, Mark joined Brighton for £20,000 with additional payments if Brighton make the play-offs. In October 1999, Mark requested a transfer as he was fed up with barracking from Brighton fans whilst he could not be guaranteed first team action due to the form of fellow keeper Mark Ormerod

Despite regaining the Number One shirt at Brighton and becoming first choice keeper, Mark took full advantage of the Bosman transfer ruling to move to ambitious Cardiff City in July 2000. Cardiff gained promotion to Division Two in April 2001 with Walton making 40 appearances in his first season. However the arrival of Neil Alexander and then Martyn Margetson pushed Walton down the pecking order so that he made just 2 appearances in 2001/02 and none so far in 2002/03. He did though win an FAW Premier Cup winners' medal. The arrival of Arran Lee-Barratt In March 2003 caused further doubts over his future at Ninian Park which were justified when he was released by the Bluebirds at the end of May 2003 following their promotion to Division One.

In March 2004, Mark signed for Australian side Bentleigh Greens who play in the Victoria Premier League.

As of September 2013, he works for Cricket Wales as a researcher and community coach, whilst studying for a Masters degree in Sports Psychology at Cardiff Metropolitan University.