A Dinamo Zagreb youth star, he made his professional debut for the club in 2019, and went on to win two league titles as well as the Croatian Cup.

He moved to Bundesliga club RB Leipzig in 2021, where he won two DFB-Pokals, before he was signed by Manchester City in 2023 for £77 million, making him the most expensive defender in footballing history.

[6] Initially, he played as a left-back or a central midfielder until Dinamo academy coach Dalibor Poldrugač moved him to the centre-back position.

Soon after, Gvardiol started drawing interest from prominent European clubs,[6] including Manchester City, Lille, Borussia Dortmund, RB Leipzig, Bayern Munich, Ajax, Inter Milan and Roma.

[7][8][9][10] He played a key part in Dinamo's 2018–19 UEFA Youth League campaign,[11] where they reached quarter-finals before losing 4–2 to Chelsea in a penalty shootout.

[14] Gvardiol made his league debut for the senior Dinamo team on 18 October in a 4–2 victory over Gorica, coming on for Mario Gavranović in the 87th minute.

That made him the sixth youngest league goalscorer for Dinamo, after Alen Halilović, Mateo Kovačić, Niko Kranjčar, Ante Ćorić and Tin Jedvaj.

[16] On 12 February 2020, in a UEFA Youth League play-off against Dynamo Kyiv, Gvardiol successfully converted a penalty in a shootout as Dinamo won 4–3 and qualified for the round of 16.

[20][21] On 26 August, in the Champions League qualifier against CFR Cluj, Gvardiol came on for Mario Gavranović in the 54th minute following Kévin Théophile-Catherine's red card.

The game led to a penalty shootout, with Gvardiol successfully converting his attempt, as Dinamo won 6–5 and progressed to the third qualifying round.

[35][36] On 10 December, Gvardiol scored his first goal in a senior UEFA competition, as Dinamo defeated CSKA Moscow 3–1 in the Europa League.

[56] By the end of the season, Gvardiol helped Leipzig win the DFB-Pokal and reach the semi-finals of the Europa League, accomplishing both feats for the first time in the history of the club.

[68][69] Gvardiol made his Premier League debut for Manchester City on 11 August in a 3–0 victory over Burnley, coming on for Rico Lewis in the 79th minute.

He was given his first Manchester City start in the 2023 UEFA Super Cup against Sevilla, playing the full 90 minutes, with his team winning 5–4 in a penalty shoot-out after a 1–1 draw in regulation time.

[72] He scored his first Manchester City goal on 9 April 2024, in the first leg of the Champions League quarter-final against Real Madrid, which ended in a 3–3 draw at the Santiago Bernabéu.

[74] On 11 May, Gvardiol scored the first brace of his career to help City overtake Arsenal in the Premier League title race with a 4–0 away win at Fulham.

[78] Gvardiol earned his first call-up to Croatia national under-21 team in October 2019, at the age of 17, when coach Igor Bišćan listed him in the squad for Under-21 Euro 2021 qualifiers against Lithuania and the Czech Republic.

[95] A day later, in a Bundesliga match against Freiburg, Gvardiol broke his nose after colliding with Willi Orbán and prominently wore a face mask during the tournament as a consequence.

[118] On 18 November 2024, in a 1–1 group stage draw with Portugal, Gvardiol scored the equalizer and secured Croatia a spot in the 2024–25 UEFA Nations League quarter-finals.

[119] Gvardiol has been described as a modern-day centre-back who can perform all the necessary defensive tasks of a traditional defender while also providing his team with serious ball progression when in possession.