PAS Giannina Born in Athens, Mavropanos began his career with the youth side at
Apollon Smyrnis, where he stayed for eight years. When he was released from Apollon, he joined
Super League side
PAS Giannina in January 2016, signing a three-and-a-half-year contract. The transfer was completed after actions of PAS former owner Giorgos Christovasilis. Both of them hail from the village Agnanta
Artas. Mavropanos made his competitive debut for PAS Giannina in the
Greek Cup on 29 November 2016. He started and played the full match as they won 1–0. Mavropanos made his league debut for PAS Giannina on 5 April 2017 against
Veria. He started and played 57 minutes as PAS Giannina lost 3–0. He scored his first goal for the club on 19 August 2017 during the first league match of the season against
Asteras Tripolis. His 19th-minute goal would be the winner in a 2–1 victory. Mavropanos was then voted man of the match in PAS Giannina's draw against
ΑΕΚ Athens a week later on 27 August. On 15 January, Mavropanos helped the Arsenal U-23 team beat Manchester United's reserves 4–0 at home, playing the entire 90 minutes. On 2 February, Mavropanos was added to the
Europa League squad for the
knockout phase. On 29 April, Mavropanos made his Premier League debut in a 2–1 defeat against
Manchester United at
Old Trafford. His performance was praised by both fans and pundits. He made his home debut in the club's next match against
Burnley. That match was also the final home game under manager
Arsène Wenger, with Mavropanos keeping his first clean sheet as the team won 5–0. He also played in the following game away against
Leicester City, but was sent off after 15 minutes to conclude his first season at Arsenal. At the beginning of October 2018, Mavropanos suffered a groin injury and was ruled out until mid-December. On 15 January 2019, he returned to competitive action after nearly four months, playing 70 minutes of the U-23s' 5–1 win over Manchester City. On 3 February 2019, he made his
2018–19 season debut as a substitute for
Shkodran Mustafi in a 3–1 away loss against champions
Manchester City. On 12 May 2019, on the last matchday of the season, Mavropanos was partnered with
Shkodran Mustafi as centre-back, but was replaced by
Laurent Koscielny after half an hour due to injury in a 3–1 away win against
Burnley.
Loan to 1. FC Nürnberg On 13 January 2020, after struggling for match time at Arsenal, Mavropanos moved to
2. Bundesliga club
1. FC Nürnberg on loan for the remainder of the 2019–20 season, and the Greek international picked up momentum in the heart of the Nuremberg defence with three stellar performances in a row. He won consecutive Man of the Match awards in his second and third game for the club, before making a key goalline clearance in his fourth. On 25 February 2020, Mavropanos picked up an injury playing against
Darmstadt 98; the club was unsure of how long he would be absent.
Loan and permanent move to VfB Stuttgart On 16 July 2020, Mavropanos signed a new deal with Arsenal and joined
VfB Stuttgart on a €250,000 loan for the 2020–21 season. At Stuttgart he was reunited with Sven Mislintat who had originally scouted and signed the player for Arsenal. On 3 October 2020, Mavropanos made his competitive debut for Stuttgart in the
Bundesliga against
Bayer Leverkusen; the game ended in a 1–1 draw. On 15 October 2020, Mavropanos suffered an injury during a friendly with
SC Freiburg and underwent an operation on his meniscus. On 24 June 2021, his loan deal was extended for a second season, with an option to make the loan permanent with a purchase option of €3.5 million at the end of the season. On 7 August 2021, a week before hosting
Greuther Fürth for the Bundesliga premiere, Mavropanos scored a header from a corner kick against
BFC Dynamo as he started the first round of the
DFB-Pokal. On 28 August 2021, Mavropanos scored his first Bundesliga goal as he battled his way through three defenders before exchanging passes with
Hamadi Al Ghaddioui and sent a fine finish into the top corner in a home
Bundesliga game against
SC Freiburg. On 2 October 2021, with an hour played, Mavropanos collected the ball on the right, burst through the
Hoffenheim defence, and unleashed a fierce left-footed drive to double Stuttgart's advantage in a 3–1 home
Bundesliga win. On 16 October 2021, the Greek central defender opened the scoring in the 15th minute with a shot from 30 meters and against the flow of the match, eventually sealing a 1–1 away draw against
Borussia Mönchengladbach. On 11 December 2021, he opened the score with a tremendous kick in a vital away 2–0 win against
VfL Wolfsburg in the club effort to avoid relegation. This was the fourth goal of the season for the defender. After the German club avoided relegation in May 2022, a purchase option for Mavropanos with a contract until June 2025 at Stuttgart was triggered.
West Ham United match against
TSC Bačka Topola On 22 August 2023, it was announced that Mavropanos had signed for English club
West Ham United on a five-year contract for a €25 million fee. 10% of the transfer fee was payable to Arsenal as they had inserted a sell-on clause in the player's contract when he was sold in 2022. He is the first
Greek player to play for West Ham. He made his debut for the club on 21 September in 3–1
Europa League win over
TSC Bačka Topola. On 28 December, he scored his first goal for West Ham in a 2–0 away win against his former club Arsenal. Mavropanos scored the winning
penalty kick to take West Ham to the
FA Cup quarter-finals against
Brentford on 9 March 2026. Later that week, on 14 March, he scored his second Premier League goal, leading to a 1–1 draw against
Manchester City. The goal was later given the West Ham goal of the month award for March. On 10 April, Mavropanos scored his third and fourth Premier League goals, in West Ham’s 4–0 win over
Wolverhampton Wanderers. ==International career==