[2] After a year playing youth and reserve football, Dunn was made a squad number as cover for Lee Harper in the 2005–06 season by then manager Colin Calderwood.

[3] Bunn was sold near the end of the 2008 summer transfer window to Blackburn Rovers, which meant Dunn was selected as first choice for the forthcoming season.

This took him to third place in the record number of minutes without conceding a goal for Northampton Town behind Alan Starling and Len Hammond.

[10] In February that season Dunn was nominated for the PFA League 2 Player of the Month award, but lost out to Wayne Brown before suffering an injury that kept him out for three weeks.

[16] Later that season, Dunn was awarded the PFA Fans Player of the Month for December after consecutive clean sheets and impressive performances.

[2] Following this, Dunn continued to remain as a first choice goalkeeper until he suffered a head injury that saw him substituted just eight minutes in against Bury on 9 April 2011.

[17] Dunn made his return to the first team on 30 April 2011, where he wore a protective mask, and kept a clean sheet, in a 2–0 win over Stevenage.

[22] Dunn made his début for the club on 10 September 2011, as a half-time substitute for Joe Murphy in a 2–0 win against Derby County.

[23] He also made another sub appearance, where he continued to help the club keep a clean for the remaining 15 minutes, in the 1–0 win over Nottingham Forest on 15 October 2011.

[26][27] It wasn't until the last game of the season on 27 April 2013 when he made his first Coventry City league start, in a 2–2 draw against Notts County.

[45] On 23 January 2015, Dunn played a vital role in the club's shock FA Cup 4th Round 0–0 draw with Manchester United, forcing a replay with the Premiership side.

[48] However, in a 1–0 loss against Wycombe Wanderers on 29 September 2015, Dunn received a straight red card in the 53rd minute after fouling Gozie Ugwu in the penalty box.

[53] On 22 July 2016, Dunn joined National League side Wrexham on a one-year deal as a player and goalkeeping coach.

[58] On 5 November 2016, Dunn made his first team return since August, where he played 68 minutes, in a 0–0 draw against North Ferriby United.