AEK Athens On 21 June 2005 Papastathopoulos joined
AEK Athens from Apollon Petalidiou after being scouted by
Toni Savevski. On 26 October 2005, he made his debut for AEK in a
Greek Cup match against
PAS Giannina, scoring in the seventh minute of the game to help lead AEK to a 3–0 win. In January 2006, he was loaned to
Beta Ethniki club
Niki Volos for six months to gain first-team football experience. He made 15 appearances for Niki Volos. During the
2006–07 Super League Greece, Papastathopoulos managed to make 14 appearances whilst competing against the likes of
Bruno Cirillo,
Traianos Dellas and
Vangelis Moras. In AEK Athens'
2006–07 UEFA Champions League campaign, Papastathopoulos managed to play in three out of six group games. In these three games, AEK managed one win (the famous 1–0 victory over
A.C. Milan, where he man-marked
Filippo Inzaghi), one draw (the 2–2 away draw with
Anderlecht) and one loss (the 3–1 away defeat to
Lille). During the
2007–08 Super League Greece, he was a mainstay in AEK's defence, keeping out competition from
Geraldo Alves. He also played in the
2007–08 Champions League campaign, and in a Super League match, he became AEK's youngest-ever captain (age 19) in a game against
Athens' local rival
Panathinaikos in 2008.
Genoa On 1 August 2008, Papastathopoulos agreed to transfer to
Genoa of the Italian
Serie A for an undisclosed fee. He also played a club friendly against Genoa on the same day. He made his debut for Genoa on 27 September 2008 against
Fiorentina, followed by a start against
Ravenna in the
Coppa Italia a few days later. His first goal for Genoa came on 5 October 2008 at home against
Napoli. Genoa won the game 3–2, but Papastathopoulos was sent off in the 89th minute During the
2009–10 season, he managed to play in most games and gained a following.
AC Milan On 20 July 2010, the AC Milan website confirmed that Papastathopoulos had joined the team, after Genoa and Milan reached an agreement to transfer Papastathopoulos to the club for €14 million, with the following payment schedule:
Gianmarco Zigoni (half of his registration rights, valued at €3.75 million),
Nnamdi Oduamadi (half of his rights, valued at €3.5 million) and
Rodney Strasser (half of his rights, valued at €2.25 million) in a
co-ownership deal, plus €4.5 million. Papastathopoulos was the club's first arrival under new manager
Massimiliano Allegri. On 24 May 2011, Milan and Genoa executives
Adriano Galliani and
Enrico Preziosi, respectively, verbally agreed to settle the player ownerships (subject to player agreements) of
Kevin-Prince Boateng,
Alberto Paloschi,
Marco Amelia and
Giacomo Beretta. The deal entailed that Milan buy back Gianmarco Zigoni, Rodney Strasser and Nnamdi Oduamadi (all under original price),
Werder Bremen in 2012 On 21 July 2011, Papastathopoulos moved to the Germany club
Werder Bremen on a loan deal until the end of the
2011–12 season, with the option to purchase outright. Following impressive performances on loan, on 16 April 2012, it was announced that Papastathopoulos would join Bremen on a permanent basis for a €5 million transfer fee. The
2012–13 season, however, was not a good one for the club. In March 2013, in the midst of a relegation battle and with tensions high, Papastathopoulos engaged in a training ground brawl with teammate
Marko Arnautović. Bremen would ultimately finish the year in 14th, staving-off relegation.
Borussia Dortmund On 24 May 2013, the eve of the
2013 Champions League Final between
Bayern Munich and
Borussia Dortmund, Papastathopoulos completed a €9.5 million transfer to Dortmund, agreeing to a five-year contract through to 2018. Upon signing, he spoke about the deal, saying, "Money did not play a role in my decision to join Dortmund. My own future was all that mattered and I am convinced that I made the right decision." With centre-back
Felipe Santana departing Dortmund for
Schalke 04, Papastathopoulos began as the effective third-choice behind tandem
Neven Subotić and
Mats Hummels. Borussia Dortmund Sporting Director
Michael Zorc expressed his satisfaction with the deal: "We are delighted that Sokratis has decided to join Borussia Dortmund. He is a flexible player capable to play in a variety of positions in defence who we believe has tremendous potential." On 10 July 2013, Papastathopoulos made his debut for Dortmund in a pre-season friendly away to Swiss club
Basel at
St. Jakob-Park, along with fellow BVB debutants (and future Arsenal teammates)
Pierre-Emerick Aubameyang and
Henrikh Mkhitaryan. On 27 July, he won his first title with the club after entering the match as a substitute in a 4–2 win over Bayern Munich for the
2013 DFL-Supercup. On 1 November 2013, he scored his debut goal for Dortmund in a win over
VfB Stuttgart in the
Bundesliga, 6–1. Papastathopoulos' strong first year with Dortmund was rewarded with his selection to the best XI of the
2013–14 Bundesliga campaign. The selection was organised in a worldwide fan vote by the governing body of the Bundesliga through its official website. The description of his play following his nomination was, "The definition of defense falls on him. The Greek stopper took advantage of the opportunities given to him by the absence of Neven Subotić and Mats Hummels. Stable, with leadership characteristics and tendency to win the ball without making easily a mistake." In November 2014, Papastathopoulos was out of action for two weeks diagnosed with a broken fibula. He suffered the injury to his right leg in Dortmund's 1–0 win over
Borussia Mönchengladbach, a result that ended a five-match Bundesliga losing streak for the club. After an early recovery, he was deemed fit for BVB's
Champions League match against
Arsenal on 26 November. On 3 January 2015, football news website Goal.com assessed statistics to determine which players maintained the highest tackle success rate in the first half of the 2014–15 season across
Europe's top five leagues; Papastathopoulos finished joint-third, alongside
Hamburger SV's
Matthias Ostrzolek, having won 92.59 per cent of all tackles. In the summer of 2015, Papastathopoulos was linked with moves to various English
Premier League clubs as Dortmund prepared for a new start following long-time manager
Jürgen Klopp's departure. Dortmund Sporting Director
Michael Zorc, however, said Papastathopoulos would still have a part to play for BVB in new manager
Thomas Tuchel's debut season with the club. On 26 October 2015, Papastathopoulos extended his contract with Borussia Dortmund until 2019. After the extension, Zorc said, "We are very pleased that we have been able to sign with Sokratis, another top performer, on a long term." During Tuchel's tenure, Papastathopoulos was promoted to be partner-in-chief to
Mats Hummels over
Neven Subotic. On 19 December 2015, Papastathopoulos scored his first goal in the
2015–16 Bundesliga in an eventual 2–1 away loss to
1. FC Köln, giving his club the lead in the first-half from a header from a corner. On 30 January 2016, in a league game against
Ingolstadt 04, Papastathopoulos reached his 100th Bundesliga appearance with Dortmund. On 22 February 2016, Papastathopoulos missed the second leg of the
UEFA Europa League round-of-32 tie against
FC Porto and the Bundesliga clash with Bayern Munich due to an adductor injury, as tests confirmed that the 27-year-old would be out for up to three weeks. The Greek centre back picked up the injury during Dortmund's 1–0 win against
Bayer Leverkusen and was replaced 13 minutes from time at the BayArena. On 21 May 2016, Papastathopoulos featured in his third
DFB-Pokal final in a row, putting in a tremendous performance despite a missed penalty, but he did not succeed in winning the DFB-Pokal for first time in his career. He started the
2016–17 season as the undisputed leader in BVB defence. On 15 September 2016, he netted the second goal in an away crashing 6–0 against
Legia Warsaw on a Group
UEFA Champions League match. On 4 January 2017, the German magazine
"kicker" listed the Greek international as one of the best players in the German
Bundesliga. The magazine paid a tribute to the best players currently playing in the German Bundesliga, separating them out into different categories. In the first category (World Class) no defenders were listed, however, Papastathopoulos was one of three defenders listed in the second category, International Class. The other two defenders included
Mats Hummels of Bayern Munich and
Jonathan Tah of Bayer Leverkusen. in 2017 On 8 February 2017, in a DFB-Pokal home win on penalties' game against
Hertha Berlin, Papastathopoulos' two quickfire (in a minute) bookings for dissent saw Dortmund finish extra time with 10 men before
Fabian Lustenberger,
Vladimír Darida and
Salomon Kalou all missed from the spot, rendering
Christian Pulisic's miss irrelevant. On 25 February 2017, Dortmund made three changes from last weekend's 3–0 win over
VfL Wolfsburg and it was two of those, Papastathopoulos and
Raphaël Guerreiro, who combined to open the scoring in the 13th minute in a 3–0 away win against
SC Freiburg. Papastathopoulos looked to be offside as Guerreiro swung in a free-kick from the right, which the Greece defender met with a header planted inside the right-hand post. On 16 April 2017, Papastathopoulos was the one who had a quick reaction to an
Eintracht Frankfurt equalising, by scoring a goal after
Sven Bender's assist giving a lead to the score in his team in a final 3–1 home win. On 26 April 2017, helped Borussia Dortmund to a 3–2 win over Bayern Munich and their fourth consecutive DFB-Pokal final. On 20 May 2017, Papastathopoulos reached 100 appearances with Dortmund in
Bundesliga in a home game against
Werder Bremen and secured automatic qualification to the group stage of next season's UEFA Champions League. On 27 May 2017, in his fourth DFB-Pokal final in a row, Borussia Dortmund claimed a first DFB-Pokal win since 2012 as
Pierre-Emerick Aubameyang's penalty defeated
Eintracht Frankfurt 2–1. On 5 August 2017, as the captain of the club, he lost the
2017 DFL-Supercup on penalties' game against Bayern Munich. On 17 September 2017, he scored at the end of the first half against
1. FC Köln, giving a lead of two goals in his club. It was his first goal for the
2017–18 season and was secured with the use of VAR (Video Assistant Referee) method. On 14 October 2017, Borussia Dortmund's unbeaten start to the season was ended by
RB Leipzig's 3–2 away win, as the Greek defender initially in trying to push the ball away helped Leipzig winger
Yussuf Poulsen to score, while at the beginning of second half, was sent off for a foul in the box and
Jean-Kévin Augustin scored the penalty. On 17 October 2017, after losing its UEFA Champions League opening games in Group H to
Tottenham Hotspur and
Real Madrid, Dortmund needed a win to kick-start its campaign in Europe's premier club competition, but they succeeded only to seal an away draw against Cypriot champions
APOEL, as the Greek defender equalised with a header to
Mario Götze's cross. On 4 November 2017, in the derby against rivals
Bayern Munich he suffered a leg injury, during the first half, and was substituted by
Jeremy Toljan, and two weeks later in an away game against
VfB Stuttgart has received a heavy blow and replaced at the end of the first half from
Dan-Axel Zagadou.
Arsenal On 2 July 2018,
Arsenal announced that Papastathopoulos had agreed a long-term contract with the club for a reported fee £17.6 million and would wear the number 5 shirt. On 12 August 2018, he made his official debut with the club as a starter at
Emirates Stadium, in a 2–0 loss against champions
Manchester City. On 4 October 2018, Papastathopoulos scored his first for the club, setting the
Gunners on their way to a comfortable 3–0 victory over
Qarabag in the
2018–19 UEFA Europa League group stage: after just four minutes of play in
Baku, the centre-back was left unmarked inside the opposing penalty area, deflecting the ball home after an initial header fell into his path. Papastathopoulos was named to the UEFA Europa League Team of the Week. On 15 October 2018, Papastathopoulos was forced off during Greece's 2–0 defeat to
Finland and was believed to have sprained his ankle. Papastathopoulos was at the heart of
Unai Emery's defence since the Spaniard took over the reins in the summer and a fixture in a winning run of nine matches. On 21 February 2019, he netted his second goal as an Arsenal player, taking advantage of a missed punch from
BATE Borisov's goalie
Denis Scherbitskiy to head the ball into an empty net following a corner kick from
Granit Xhaka, to seal a 3–0 home win for Arsenal and send them through to the Round of 32 in the
2018–19 UEFA Europa League. On 12 April 2019, Papastathopoulos was named to the
UEFA Europa League's 'Team of the week' after playing a vital role in Arsenal's 2–0 win over
Napoli in the
first leg of the quarter-finals. He was one of four Arsenal players selected along with
Petr Čech,
Ainsley Maitland-Niles, and
Aaron Ramsey. On 24 April 2019, Papastathopoulos scored his maiden goal in the English
Premier League via a close-range header from a corner kick, but Arsenal slipped to a 3–1 defeat against
Wolverhampton Wanderers. On 29 May 2019, he started in the
2019 UEFA Europa League Final against
Chelsea which Arsenal lost 4–1. This was the first time Arsenal had conceded four goals in a European match since a 5–1 loss to Bayern Munich in March 2017. On 27 October 2019, Papastathopoulos – marking his 50th appearance – scored his first goal of the season, after
Crystal Palace failed to clear
Nicolas Pépé's corner in a 2–2 draw at home. On 1 January 2020, he scored a close-range finish to seal a 2–0 win over
Manchester United, securing
Mikel Arteta his first victory in charge of the
Gunners. He was named
Sky Sports Man of the match. On 2 March 2020, he scored with a volley to give Arsenal the lead in a 2–0 away win against
Portsmouth, helping Arsenal to be the first team in the
FA Cup quarter-finals. On 1 August 2020, Papastathopoulos played as a late substitute in the
2020 FA Cup Final against Chelsea, as Arsenal won the trophy for the 14th time. Papastathopoulos and
Mesut Özil were notably excluded from Arsenal's Premier League and Europa League squads for 2020–21, leaving them only eligible for one League Cup game between October and January. On 20 January 2021, Arsenal announced that Papastathopoulos would be leaving the club after his contract was cancelled "by mutual consent."
Olympiacos On 25 January 2021, Papastathopoulos joined Greek side
Olympiacos on a two-and-a-half-year contract. On 21 April 2021, he scored his first goal with the club, in a 1–0 home win game against
Asteras Tripolis.
Real Betis and retirement On 26 October 2023, after leaving Olympiacos at the end of his contract, Papastathopoulos signed a one-year deal with
La Liga club
Real Betis. On 19 May 2024, Papastathopoulos announced that he would retire at the end of the season. Papastathopoulos played his last professional game against
Real Madrid at the
2023–24 La Liga final round. ==International career==