He was appointed player-manager of Southern League Premier Division club Tamworth in 2001, before leaving to join the coaching staff at Coventry City in 2002.

[13] He made 31 appearances, scored 5 goals and recorded 7 assists in the 1982 North American Soccer League season as Seattle finished first in the Western Division.

[23][24] He started for Seattle in Soccer Bowl '82 before being substituted for Roger Davies, and the match was won 1–0 by the New York Cosmos with a 31st-minute goal scored by Giorgio Chinaglia.

[33] Mills signed for Second Division club Leicester City on 2 March 1989 as part of the deal that saw Phil Turner join County for a fee of £125,000, with over two months of 1988–89 remaining.

[38][41] This season saw an improvement in fortunes for Leicester, as they reached the Northern Area final of the Full Members' Cup, in which they were beaten 3–1 on aggregate by Nottingham Forest, and the Second Division play-offs with a fourth-place finish the league.

[41] Mills captained the Leicester team that reached the First Division play-offs in 1992–93 with a sixth place league finish, and they beat Portsmouth 3–2 on aggregate in the semi-final.

[44] By finishing fourth in the table Leicester made the First Division play-offs for the third successive season, and Mills led the team out before the final despite being unable to play.

[47] Making his debut in a 2–0 away defeat to Reading in the First Division on 1 October 1994, he played regularly at right-back before moving to left-back towards the end of 1994–95 after Craig Short returned to the team.

[48][49] He picked up his last playing honour this season as part of the team that won the Anglo-Italian Cup after County beat Ascoli 2–1 in the final at Wembley Stadium.

[60] However, Mills resigned a week after the season ended in May 1998 as the club's takeover by local businessman Reg Brealey would have meant dismantling the team due to budget cuts.

[78] Tamworth missed out on promotion to the Football Conference on the final day of 2001–02, finishing second in the Southern League Premier Division, two points behind the title winners Kettering Town.

[32] His first match in charge came just a day later, in which Marc Goodfellow scored a stoppage time winner for Bristol City as County were beaten 2–1 at home.

[96] His first match as Alfreton manager was a 2–1 home defeat to Vauxhall Motors on 13 August 2005,[97] and having flirted with relegation the team finished the season in 17th place in the Conference North.

[103] After an undisclosed financial settlement was agreed Mills left Alfreton to return to Tamworth, who at this time were in the Conference National, for a second spell as manager on 26 January 2007.

[109] Mills was given time to rebuild the squad over the summer of 2008, bringing in players like Bradley Pritchard, Alex Rodman, Chris Smith, Tom Shaw and Michael Wylde.

[109] He was named the Conference North Manager of the Month for September 2008, in which Tamworth achieved three straight league wins following a draw away to in-form Alfreton.

[81] He made the last appearance of his career aged 48 after starting Tamworth's 4–3 home defeat to Ebbsfleet United on 24 April 2010, before substituting himself for Des Lyttle in the 55th minute.

[108] With a compensation package agreed Mills left Tamworth after being appointed the manager of fellow Conference Premier club York City on 13 October 2010.

[122][123] He was not registered as a player at York, although chairman Jason McGill would refuse [citation needed] Mills a playing contract on multiple occasions.

[123][124][125] In the third round of the competition Mills' York played Premier League team Bolton Wanderers, who won 2–0 with late goals from Kevin Davies and Johan Elmander.

[123][127] York finished 2010–11 in eighth place in the Conference Premier,[123] The Press claiming Mills "restored pride and belief into the club" with his "unbounded optimism and positivity".

[131] The team played a passing style in the first half of the season, before often grinding out results with The Press saying they "compensated for a loss of craft with bundles of graft".

[132] After beating Mansfield Town 2–1 on aggregate in the play-off semi-final,[131] York were 2–0 victors over Newport County at Wembley Stadium in the 2012 FA Trophy Final; this was the first time the club had won a national knockout competition in its 90-year history.

[132] This on-field achievement, combined with the approval for a community stadium to be built for the club, led to The Press lauding "an unsurpassed nine days in the Minstermen's proud existence".

[136] Mills returned to management with Conference Premier club Gateshead, signing a one-year rolling contract on 3 September 2013 to replace Anth Smith who resigned in August.

[142][143] Gateshead's form continued to improve and by mid January 2014 they had moved into a play-off place;[141] Mills commented in February that "When I came in, I wanted everyone here to believe that we could win promotion – I think they're starting to now".

[145] With a 4–2 aggregate win over Grimsby Town in the semi-final, Gateshead played at Wembley Stadium for the first time in the play-off final; despite entering the match on the back of a 14-match unbeaten run they were beaten 2–1 by Cambridge United.

[147] He was named the Non-League Manager of the Year for 2013–14 at the National Game Awards, ahead of John Still, who led Luton to the Conference Premier title.

[158] The "Steelmen" parted company with Mills immediately after their 2-0 defeat to Belper Town on the final day of the Northern Premier League Midlands season, having finished 15th.

[161] He prefers to employ a 4–3–3 formation, explaining it allows his teams to play entertaining football and makes them hard to beat, and it brought him success when at Tamworth and York.