Clark captainedEngland at under-18, under-19 and under-20 level, but in October 2010 declared his ambition to play for theRepublic of Ireland, the country of his parents' birth.[5] He was called up to the national team a month later for the friendly match againstNorway, and made his full debut againstWales on 8 February 2011.[6]
Clark was born inHarrow, London,[2] and grew up inSandy, Bedfordshire. He came through theAston Villa youth academy after joining at the age of eleven, and captained the academy U18 team to the2007–08 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's2008–09 UEFA Cup match away atCSKA Moscow, but remained an unused substitute. He captained the reserves to thePremier Reserve League South title and defeated PRL North winners Sunderland in the play-off final to win their first ever Reserve League trophy.[7]
Clark was included in the squads for the pre-season friendlies and the2009 Peace Cup.[8] On 30 August 2009, he made his debut in a 2–0 win againstFulham. WithCurtis Davies unavailable through injury, the 19-year-old was named in Villa's starting line-up, partneringCarlos 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 theBBC named the youngster in his team of the week.[10] Although the formidable partnership of new signingsJames Collins andRichard 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]
Clark started in the first two league games of the 2010–11 season: againstWest Ham United, partnering Richard Dunne and keeping a clean sheet; then againstNewcastle United. Clark was also handed a start inGérard Houllier's first match as new Villa manager, againstBlackburn Rovers in theLeague Cup. He then started the match against local rivalsBirmingham City in midfield and continued in the role againstFulham andBlackpool 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 againstArsenal 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]
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]
On 25 August 2012, he was sent off againstEverton for a professional foul onNikica Jelavić. On 3 September 2012, he scored his first goal of the season in a 1–1 draw away toNewcastle 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 toStoke, afterGabriel Agbonlahor who had started the match as captain was replaced byDarren 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 atNorwich which saw Villa qualify for the semi-finals.[citation needed]
Clark started Aston Villa's first game in their 3–1 away victory atArsenal. 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-mateLibor Kozák.[14] The mishandled injury[15] virtually ended Kozák's Premier League career.[16]
Aston Villa began the 2014–15 season in good form withPaul Lambert re-introducingAlan Hutton, forming a new look back four of Alan Hutton,Ron Vlaar,Philippe Senderos andAly 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 withJores Okore and formed a solid partnership. Clark scored his first goal of the season from a free-kick curled in byAshley Westwood in a 2–1 home victory overLeicester.[17]
On 3 August 2016, Newcastle announced that they had completed the signing of Clark.[18] Having established himself alongside club captainJamaal Lascelles in central defence, he scored his first goal for the club in a 6–0 win againstQueens Park Rangers on 13 September 2016.[19] He went on to add further goals againstBrentford andBristol City while also helping Newcastle concede the joint-lowest number of goals in the division as they returned to thePremier League at the first time of asking. He remained a regular starter for Newcastle in league games for the first half of the following season. However, he was left out of the side for most of the second half of the season withFlorian Lejeune andJamaal Lascelles being preferred at central defence. In the 2018–19 season he only managed 8 appearances in the first team in the Premier League; however he still managed to score three goals, againstArsenal,Burnley, andChelsea respectively.[20]
In November 2019 he said he had previously considered leaving Newcastle United in order to maintain his place in the Irish international set-up.[21]
On 20 January 2021, Clark extended his contract with Newcastle, signing a new two-and-a-half-year contract.[22] On 30 November 2021, Clark was sent off after just nine minutes in a home game againstNorwich.[23]
Following his release by Newcastle, Clark joinedStoke City on 10 October 2023 on a deal until the end of the2023–24 season.[26] Clark made three appearances for Stoke of which all came in the final three games underAlex Neil which all were lost.[27] Clark was not selected by new managerSteven Schumacher and left the club at the end of the season.[28]
Clarkcaptained theEngland U19 team through qualification for the2008 UEFA European Under-19 Championship, playing in five out of the six qualifiers and scoring a goal. He missed out on the tournament through an ankle injury sustained during training.[29][30] After being promoted to theEngland U20s, he was appointed captain and scored in only his second match, in a friendly against Italy in March 2008.
In late September 2010,Football Association of Ireland (FAI) officials approached Clark about switching his allegiance. They sentscout and formerRepublic of Ireland under-21 manager,Don Givens, to watch him in the match against Blackburn.[31] On 5 October 2010, it was reported that Clark had pledged his international future to the Irish national team as he qualified through his Irish parents. Club teammateRichard Dunne played a role in convincing him and had spoken to FAI scouts about his eligibility.[32] On 12 November 2010, Clark was named in the Republic of Ireland squad for the friendly againstNorway.[33] He then made his debut on 8 February 2011 againstWales at theAviva Stadium.[34] On 6 February 2013, Clark scored his first goal for the Republic of Ireland, helping them to a 2–0 friendly victory againstPoland.[35]
In Republic of Ireland's opening match atEuro 2016 againstSweden, Clark deflected a ball fromZlatan Ibrahimović into his own net to level the scores.Wes Hoolahan had earlier given Ireland the lead but Clark's mishap saw them share the spoils as the match ended 1–1.[36]
In November 2019, he said he had previously considered leaving Newcastle United in order to maintain his place in the Irish international set-up.[21]