Parnaby joined Birmingham City in 2007 and helped them win promotion to the Premier League as runners-up in the 2008–09 Championship.

[7] Parnaby made his first-team debut for Middlesbrough in September 2000 in a League Cup match against Macclesfield Town.

[29] It was Parnaby's shot in the semi-final second leg against Arsenal which was deflected in by José Antonio Reyes to seal the win for Middlesbrough.

[31] Parnaby started the 2004–05 season playing regularly in Middlesbrough's team before he broke his leg during training in October 2004, which was expected to keep him out of action for around three months.

[35] After getting playing time for 10 matches,[36] he suffered an injury that kept him out for a week before making his return on 29 April, coming on as a substitute in a 1–1 draw away to Liverpool.

[42] He scored his first Middlesbrough goal on 17 January 2006, in a 5–2 home win over Nuneaton Borough in the fourth round of the FA Cup.

[55] Parnaby signed a three-year contract with newly promoted Premier League club Birmingham City on 1 June 2007 on a free transfer.

[56] He revealed that manager Steve Bruce was the main factor in joining Birmingham, stating he made him feel "10 feet tall".

[6] Parnaby made his debut on 12 August in the opening match of the 2007–08 season, coming on as a substitute for Queudrue in the 51st minute of a 3–2 away loss against Chelsea.

[57][58] As the season progressed, he struggled with injuries and loss of form,[59] and was unable to dislodge Stephen Kelly from the right-back spot.

[68][69] Parnaby was a substitute in Birmingham's first match after their return to the Premier League, against Portsmouth, replacing Grégory Vignal in a 1–0 home victory on 19 August 2009.

[71] Parnaby struggled with back and groin injuries during the 2009–10 season, and after returning to fitness was unable to displace Stephen Carr at right-back.

[76] He made his first appearance of the season on 21 September in a 3–1 home win over Milton Keynes Dons in the third round of League Cup.

[77] Parnaby scored his first goal for Birmingham on 29 January 2011 in a 3–2 home win against Coventry City in the third round of FA Cup.

[77][78] He was an unused substitute as Birmingham won the 2010–11 League Cup, defeating Arsenal 2–1 at Wembley Stadium in the final on 27 February.

[80] He was released by Birmingham following their relegation from the Premier League at the end of the 2010–11 season,[81] in which he made 11 appearances and scored one goal.

[91] Parnaby made his return from injury to start in the opening match of the 2013–14 season, a 2–1 home loss against Leicester City on 3 August 2013.

[101] Parnaby made his debut for the England national under-16 team on 23 June 1998 when starting their 4–1 defeat to the United States (US), as part of a tour of the country.

[102] Parnaby was part of the team at the 1999 UEFA European Under-16 Championship, and played in all of their four matches before they were eliminated by the Czech Republic in the quarter-final.

[111] Parnaby joined Martin Gray's backroom staff at National League North club York City in July 2018 as strength and conditioning coach.

[116][117] Parnaby joined the coaching staff of National League North club Spennymoor Town on 9 January 2020.

[122] Ahead of the match against Brighton & Hove Albion, Middlesbrough's players wore black armbands as a mark of respect.