[11] On 15 January, Mavropanos helped the Arsenal U-23 team beat Manchester United's reserves 4–0 at home, playing the entire 90 minutes.

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.

[19] 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.

FC Nürnberg on loan for the remainder of the 2019–20 season,[21][22] and the Greek international picked up momentum in the heart of the Nuremberg defence with three stellar performances in a row.

[28] 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.

[30][31] 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.

[32] 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.

[33] 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.

[35] 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.

[40] On 24 March 2021, Mavropanos was called up to the Greek senior team by coach John van 't Schip for the forthcoming World Cup 2022 qualifiers against Spain and Georgia.