[12] He spent four years at the academy playing in the Młoda Ekstraklasa League and was regularly called up to the Poland national under-17 football team.

Zieliński made his debut in Serie A on 2 November 2012 when he replaced Antonio Di Natale in 91st minute of a match against Cagliari.

[14] On 14 April 2013, he made his first appearance in the club's starting lineup and registered an assist in Udinese's convincing 3–0 victory over Parma.

[16] On 13 August 2014, he made his official debut for Empoli replacing Daniele Croce in the 80th minute of the match against AS Roma, which ended in a 0–1 loss for his club.

[27] On 21 August 2016, he made his debut appearance for Napoli, alongside his compatriot Arkadiusz Milik, substituting Marek Hamšík in the 71st minute of the match against Pescara, which ultimately concluded in a 2–2 draw.

[29] On 13 September 2016, Zieliński made his Champions League debut in Napoli's match against Dynamo Kyiv, which concluded in his team's 2–1 victory.

Zieliński began the 2017–18 Serie A season as a starting lineup player in the match against Verona, which took place on 19 August and concluded with Napoli's 3–1 win.

[36] On 18 November 2017, he entered the pitch in the 69th minute of the match against AC Milan as a substitute for Marek Hamšík and scored the second goal in Napoli's narrow 2–1 victory.

[37] On 21 November 2017, Zieliński scored his first Champions League goal in the match against Shakhtar Donetsk, which ended with Napoli's decisive 3–0 win.

[40] On 22 February 2018, he scored his first goal in UEFA Europa League in the match against RB Leipzig, contributing to a 2–0 victory for Napoli.

[72] On 4 October 2022, he scored another Champions League goal in a match against Ajax, which concluded in Napoli's 6–1 demolition of the Dutch side.

[74] On 24 December 2023, he was named Polish Footballer of the Year beating Robert Lewandowski by 12 points and breaking his four consecutive win streak.

[75] On 7 September 2022, he scored two goals and provided one assist in a Champions League group stage match against Liverpool, which concluded in a 4–1 victory for Napoli.

[8] On 3 July 2024, Zieliński signed for the fellow Serie A club Inter Milan on a free transfer following the expiration of his Napoli contract.

[78] On 27 October 2024, Zieliński scored two goals, both from penalty kicks, in a Derby d'Italia match against Juventus, which ended in a 4–4 draw.

[81] On 23 December 2024, Zieliński entered the pitch in the second half and of the match against Como and provided an assist contributing to Inter's 2–0 victory.

[82] On 4 June 2013, Zieliński made his senior international debut for the Poland national team in a friendly match against Liechtenstein.

[83] On 31 July 2013, he was called up for a friendly match against Denmark scoring his first goal for the national team in the second half and securing a 3–2 win for Poland.

[86] On 7 September 2018, he scored a goal after an assist from Robert Lewandowski against Italy in a UEFA Nations League match that ended in a 1–1 draw.

[87] On 10 June 2019, he registered an assist to Kamil Grosicki's goal in a UEFA European Championship elimination match against Israel contributing to a 4–0 victory for Poland.

[88] On 5 March 2021, he provided an assist to Kamil Jóźwiak's goal in a FIFA World Cup elimination match against Hungary at the Puskás Aréna, which concluded in a 3–3 draw.

[90] On 23 June 2021, he provided an assist to Robert Lewandowski's goal to make it 1–2 in a UEFA Euro 2020 group stage match against Sweden, which ended in Poland's 2–3 loss.

[91] On 26 November 2022, he scored the first goal in Poland's 2–0 victory over Saudi Arabia in a group stage match at the 2022 World Cup.

[96] His consistency, the ability to read the game and crucial passes made him one of the pillars of the team during his spell at Napoli contributing to his club winning the Coppa Italia in 2020 and the Serie A title in 2023.