[4] Mills was born in Whitby, and brought up in Thornaby-on-Tees and while at school represented his country with England Schoolboys.
After school, he attracted interest from several clubs, including Hull City, Stoke City, Manchester United and Burnley, but decided on a move to local team Middlesbrough, after missing close to a year due to injury, and signed for the club in July 1968 His first team debut came as a substitute towards the end of the 1968–69 season and he scored at Swindown Town in 1969–70 on his full debut.
Two years later, his form had again caught the attention of other managers, and so in 1979, Ron Atkinson paid £518,000[5] to take him to West Bromwich Albion, breaking the English transfer record and making Mills Britain's first half million pound footballer.
[3] Mills scored on his first full appearance for West Brom, but despite the huge sum of money invested in him he was not given many opportunities to prove himself, with injuries, loss of form and a switch to midfield limiting his goals.
[5] Following a stint as assistant chief scout at Newcastle United, where he worked under seven different managers, it was announced on 29 April 2008 that Mills would return to Middlesbrough to boost the recruitment team along with Gordon McQueen.