Early career

Clark was born in Harrow, London,^[2] and grew up in Sandy, Bedfordshire. He came through the Aston Villa youth academy after joining at the age of eleven, and captained the academy U18 team to the 2007–08 Premier Academy League—the academy's maiden league title. He was given a squad number for the 2008–09 season and named on the bench for Villa's 2008–09 UEFA Cup match away at CSKA Moscow, but remained an unused substitute. He captained the reserves to the Premier Reserve League South title and defeated PRL North winners Sunderland in the play-off final to win their first ever Reserve League trophy.^[7]

2009–10 season

Clark was included in the squads for the pre-season friendlies and the 2009 Peace Cup.^[8] On 30 August 2009, he made his debut in a 2–0 win against Fulham. With Curtis Davies unavailable through injury, the 19-year-old was named in Villa's starting line-up, partnering Carlos Cuéllar in defence.^[9] He helped keep a clean sheet and nearly marked his debut with a goal but sent his header inches wide. Garth Crooks of the BBC named the youngster in his team of the week.^[10] Although the formidable partnership of new signings James Collins and Richard Dunne limited him to the bench, he was tipped to break into the first team on a regular basis within several years.^[11] In November 2009, he signed a contract extension until June 2012.^[12]

2010–11 season

Clark started in the first two league games of the 2010–11 season: against West Ham United, partnering Richard Dunne and keeping a clean sheet; then against Newcastle United. Clark was also handed a start in Gérard Houllier's first match as new Villa manager, against Blackburn Rovers in the League Cup. He then started the match against local rivals Birmingham City in midfield and continued in the role against Fulham and Blackpool due to the club's injury crisis. On 27 November 2010, Clark scored his first two goals for the club in a 4–2 defeat against Arsenal at home. He scored a 91st-minute equaliser against Chelsea on 2 January 2011 to rescue a point. He also became the only player in Premier League history to be booked in six successive appearances within the same season.^{[13][non-primary source needed]}

2011–12 season

Clark scored his first FA Cup goal for the club against Bristol Rovers on 29 January 2012, with a solo run, including stepovers and a left-footed strike curled into the bottom corner.^{[citation needed]}

2012–13 season

On 25 August 2012, he was sent off against Everton for a professional foul on Nikica Jelavić. On 3 September 2012, he scored his first goal of the season in a 1–1 draw away to Newcastle United. On 8 December 2012, after captaining Villa's youth and reserve sides, Clark was handed the armband for the senior side for the first time in a 0–0 draw at home to Stoke, after Gabriel Agbonlahor who had started the match as captain was replaced by Darren Bent. Three days later, Clark followed up his initial role as captain by performing the role again, this time for the full 90 minutes, in a 4–1 victory in the League Cup away at Norwich which saw Villa qualify for the semi-finals.^{[citation needed]}

2013–14 season

Clark started Aston Villa's first game in their 3–1 away victory at Arsenal. After a dip in his form midway through Aston Villa's season, he was dropped to the bench as Lambert preferred a partnership between Ron Vlaar and fellow academy graduate, Nathan Baker. However, due to injury constantly plaguing Aston Villa's defence, along with consistently poor results, Clark still managed 28 appearances in a season that saw Villa finish 15th on 38 points. He accumulated nine yellow cards throughout the season.^{[citation needed]}

In January 2014 during a training game Clark broke the right leg of his team-mate Libor Kozák.^[14] The mishandled injury^[15] virtually ended Kozák's Premier League career.^[16]

2014–15 season

Aston Villa began the 2014–15 season in good form with Paul Lambert re-introducing Alan Hutton, forming a new look back four of Alan Hutton, Ron Vlaar, Philippe Senderos and Aly Cissokho. When an injury ruled Vlaar out, Nathan Baker came into the back four, with Clark remaining on the bench. After injuries to both Baker and Senderos, Clark was called on along with Jores Okore and formed a solid partnership. Clark scored his first goal of the season from a free-kick curled in by Ashley Westwood in a 2–1 home victory over Leicester.^[17]

Loan to Sheffield United

On 13 July 2022, Clark joined Championship club Sheffield United on loan for the 2022–23 season.^[24] He scored his first goal for the club in a 3–1 win over Coventry City on 26 December 2022.^[25]