[9] As a boy, Miller also played Gaelic games for his hometown club Éire Óg and represented Cork GAA at youth level.

[10][11] In a web chat in 2007, Miller said that his family was his largest influence in football, and that Martin O'Neill and Sir Alex Ferguson were also influential to his career.

[14] During his time at Celtic Park, he had been on a six-month loan spell with Danish football club AGF Aarhus during the 2001–02 season, making 18 appearances without scoring a goal.

[16] Miller scored his first professional goal on 30 July 2003 in the first leg of the second qualifying round of the UEFA Champions League, coming on as a late substitute to complete a 4–0 win at Lithuania's Kaunas.

[17] Two months later in the group stage, he scored against Lyon, and subsequently manager Martin O'Neill offered him a long-term contract, attempting to keep Miller at the club.

[20] Manchester United manager Sir Alex Ferguson attended the game to scout Anderlecht's Vincent Kompany, but instead was convinced to approach Miller.

He made his United debut on 11 August as a 67th-minute substitute for Darren Fletcher in a 2–1 win at Dinamo Bucharest in the first leg of the third qualifying round of the Champions League.

[26] He scored his first goal for the club on 26 October against Crewe Alexandra in the third round of the League Cup, finishing a pass by David Bellion in a 3–0 win at Gresty Road.

He was given a rare first-team start in January 2005 in an FA Cup tie against non-league Exeter City, but turned in a poor performance and was substituted in the second half.

[7] In July 2006, The Daily Telegraph reported that Miller would be allowed to leave Manchester United, should the Red Devils receive a suitable offer.

[39] Miller scored his first Premier League goal on 22 September 2007 against North-East rivals Middlesbrough in the Tees-Wear derby; his 89th minute 20-yard left-footed shot sealed a 2–2 draw at the Riverside Stadium.

[40] He was sent off for the second time in his Sunderland career by Peter Walton; against Chelsea on 8 December for a push on Claudio Pizarro, as the Black Cats lost 2–0.

[42] He was linked with a move to Toronto FC, a Canadian club with ties to former Sunderland players Danny Dichio, Carl Robinson and Andy Welsh.

[43] Miller received interest in January 2009 as Championship club Queens Park Rangers expressed their wishes to secure a loan deal.

[51] Miller was sent off near the end of a 2–1 loss at Kilmarnock on 18 December for a foul on Conor Sammon, but on appeal the punishment was reduced to a yellow card.

[58] On 20 November, he received a straight red card in the first half of a 2–2 draw at Melbourne Victory for denying Archie Thompson a clear goalscoring opportunity.

A report from Radio Australia noted how Miller and midfield partner Jacob Burns were "outstanding in leading the Glory's well-structured and hardworking defensive set-up which stifled the Roar's fluid style", until he conceded a penalty with a foul on Besart Berisha at the end of the match, from which the Brisbane player scored the winning goal.

[64] On 30 October 2014, Miller was released by Brisbane Roar after asking to have his contract terminated following being dropped from the squad for two games with no explanation, which he found unprofessional and disrespectful.

[65][66] Eleven days after leaving the Roar, Miller signed for another A-League club, Melbourne City, on a short-term contract as a National Replacement Player in place of Aaron Mooy, joining fellow former Irish international Damien Duff.

[70] Miller was a regular in his only season at Turners Cross, in which his team finished as runners-up in the league and the FAI Cup to Dundalk, and on 19 January 2016 he chose to leave.

[84] The Gaelic Athletic Association permitted the game to be played at Páirc Uí Chaoimh in Cork, which would not normally have been allowed under GAA rules.