Liddle began his career with hometown side Middlesbrough. He was a regular in the academy sides and won the 2003–04 FA Youth Cup alongside the likes of David Wheater, Tony McMahon and Adam Johnson. Although he was handed a professional contract, he was not able to break into the first team.
In August 2006, Liddle joined nearby League Two side Hartlepool United. His ability to play in a number of positions across defence and midfield made him an attractive proposition and boss Danny Wilson was delighted to be able to prise him away from The Riverside Stadium. Liddle won the player of the season award for the 2006–07 season.
On 13 August 2011, while playing in a home league match against Walsall, Liddle suffered an injury, as his zygomatic bone became fractured in two places. He was able to complete the match, which ended in a 1–1 draw. However, he was sidelined afterwards. For his return to playing, he wore a protective mask.
On 19 May 2012, it was announced that Liddle was released from Hartlepool United after 6 years, causing many fans to question the club's leadership.
In June 2012 Liddle signed for Notts County on a two-year contract. Liddle stated that it was Keith Curle's desire to manage in the Championship that played a big part in the switch. "Keith wants wants to manage in the Championship with Notts. That's why I came here. Hopefully I can help him do that". He wore the number 8 shirt for the 2012–13 season. Before the start of the season Liddle admitted there was a challenge to earn a first team spot. "It's the most competitive squad I've ever been in, If I get the shirt I will have to play well to keep it and if I'm not in the team I'll have to work even harder in training to get in there."
He made his competitive debut for the club in a 2–1 victory over Crewe partnering Dean Leacock in the centre of defence. Liddle made a good start to his career at Notts County and was awarded the PFA Fans' Player of the Month for September, continuing to play at centre back, he ensured County remained unbeaten in that month.
Liddle made his final and 46th league appearance of the season against Coventry. It meant he had played every minute of the 2012–13 season equaling a record last set by County's Pedro Richards 30 years ago. He then won four awards at the clubs' end of season award ceremony. Including; The Manager’s Player of the Year, Players’ Player of the Year, Fans’ Player of the Year and the Supporters’ Club Player of the Year.
On 9 June 2014, Liddle signed for Bradford City on a one-year deal with the option of an additional year. Liddle made his debut for the club on 9 August, in a 3–2 win against Coventry City at Valley Parade.
Liddle signed for Chesterfield on 1 February 2016, transfer deadline day, for an undisclosed fee. He was named the club's captain. Liddle was sent off in his third appearance for the 'Spireites', on 16 February 2016 in an away game to Colchester United for an 18th minute foul. Liddle scored his first goal for the club on 13 August 2016, scoring the first in a 3-1 victory over Swindon Town, heading into an empty net after a Ched Evans free kick was saved.
On 13 January 2017, Liddle joined Carlisle United on an 18-month deal for an undisclosed fee, where he was re-united with his former manager Keith Curle.As of match played 12 September 2017