Basford, Nottingham born goalkeeper Mark Mellors played for junior club Carrington in 1899 and Bulwell United in 1901 before joining First Division Notts County, for whom he made his Football League debut at Sheffield United in April 1903. After 9 appearances for The Magpies as understudy to Harry Pennington, he joined Southern League Brighton & Hove Albion in the summer of 1904, spending three seasons at The Goldstone Ground before returning to The Football League with Sheffield United in 1907. At Bramall Lane he was understudy to Joe Lievesley, making only one appearance in February 1908 when he played in a 2-2 draw with Woolwich Arsenal.
He joined First Division Bradford City for £350 in March 1909, playing in their last seven matches which produced four wins to save them from relegation. In the last game of the season City needed to defeat Manchester United to avoid the drop. In the closing minutes he was knocked out as he threw himself into the path of a vicious drive. He was propped against the goalpost as City defended the resulting corner. Mellors was the hero of the day as City won 1-0. At the final whistle the crowd carried Mark shoulder high from the field.
Initially understudy the following season to Martin Spendiff and Harry Maskery, but he took over from Maskery in November 1910. The highlight of his career was when he kept goal in The Bantams’ triumphant 1911 FA Cup Final winning team that beat Newcastle United 1-0 in a replay at Old Trafford. Indeed he played in 7 ties in total during their successful Cup run including the Final at The Crystal Palace on 22nd April 1911 which finished 0-0 in front of nearly 70,000 spectators, and only conceded one goal. While remaining the principal glovesman for The Bantams in 1911-12, playing 31 times in the campaign, he subsequently lost his place and played his last match for Bradford City in October 1913, having made 84 appearances. He formally retired from playing in 1918.