Haller began his career in France withAuxerre, and moved on loan toEredivisie sideUtrecht in 2015, before signing on a permanent basis. Two years later, he moved to the German clubEintracht Frankfurt, winning theDFB-Pokal in 2018.Premier League sideWest Ham United signed him a year later for a club-record transfer worth €49.8 million (£45 million). Haller returned to the Netherlands in 2021, signing withAjax, for a club record fee of €22.5 million (£18.8 million). In his first six months, he won the Eredivisie and theKNVB Cup. He became the first player to score across seven consecutive UEFA Champions League matches during the2021–22 season, and then transferred toBorussia Dortmund for an initial €31 million.
Haller represented France at youth level, before switching his allegiance in 2020 to theIvory Coast. He scored on his international debut againstMadagascar, and represented the national team at theAfrica Cup of Nations in2021 and2023, scoring the winning goal in thefinal of the latter tournament.
During the2011 FIFA U-17 World Cup, on 26 June 2011, Haller signed his first professional contract withAuxerre, agreeing to a three-year deal.[7]
Ahead of the2012–13 season, Haller was promoted to the senior team bymanagerJean-Guy Wallemme. His professional debut came on 27 July 2012, in the team's openingleague match of the 2012–13 campaign againstNîmes.[8]
On 24 December 2014, it was announced that Haller was sent on loan toEredivisie clubUtrecht until the end of the season.[9] At the end of the season, it was announced that FC Utrecht had signed Haller.[10] The supporters voted for Haller as the winner of theDi Tommaso Trophy 2015, Utrecht's player of the year award.[11]
On 15 May 2017, Haller signed withEintracht Frankfurt on a four-year deal for a reported fee of €7 million.[12] In the2017–18 DFB-Pokal, he scored four goals for Frankfurt, as the club won thefinal, marking the first trophy of Haller's career. In the2018–19 Bundesliga season, he scored 15 league goals in 29 appearances as the club finished seventh.[13]In addition to his goals scored, he also made nineassists, meaning he was involved in 24 goals, a figure only beaten in the 2018–19 season byRobert Lewandowski with 29.[14]
On 17 July 2019, Haller signed withWest Ham United on a five-year deal for a club record fee, that could rise to £45 million.[15][16] He made his debut on 10 August, playing the full 90 minutes of a 5–0Premier League loss against reigningchampionsManchester City.[17] Two weeks later, he scored his first goals in a 3–1 away win againstWatford in which the latter was an acrobaticbicycle kick.[18] Haller struggled at West Ham, attributing it toDavid Moyes replacingManuel Pellegrini as manager and then preferringMichail Antonio up front, as well as the ill health of his wife and newborn son.[19]
In July 2020, Frankfurt reported West Ham toFIFA after they had failed to pay an instalment in May 2020 of £5.4 million as part of the £45 million transfer. West Ham claimed that they had withheld the payment, following a contractual dispute between the two clubs.[20] On 16 December, Haller scored an overhead kick in a 1–1 draw againstCrystal Palace that was voted as thePremier League Goal of the Month.[21]
On 8 January 2021, Haller signed a four-and-a-half-year contract with Dutch clubAjax for a club record fee of €22.5 million (£18.8 million), reuniting with his former Utrecht managerErik ten Hag.[22][23] He made his debut two days later as a second-half substitute againstDe Topper rivalsPSV, assistingAntony for the equaliser in a 2–2 draw.[24] On 14 January, he scored his first goal, and provided an assist, in a 3–1 away win overTwente.[25] On 3 February, Haller was mistakenly omitted from the club's list for the knockout stages of theUEFA Europa League and therefore would be unable to play for the club in the competition.[26]
In a 5–1 away victory overSporting CP in theUEFA Champions League on 15 September 2021, Haller scored twice in each half to become the first player to score four on his Champions League debut sinceMarco van Basten forA.C. Milan in 1992; the Dutchman had however already played in the competition under its former name of the European Cup.[27] In the following fixture 13 days later, he recorded a goal againstBeşiktaş, becoming the first player in the history of the competition to score five goals in his first two match appearances;[28] against the same team on 24 November, Haller scored twice in a 2–1 win to become the first player to score nine goals in five consecutive matches of the competition.[29] On 7 December, Haller scored in his team's Champions League group stage match, becoming only the second player to register in all six group games afterCristiano Ronaldo in2017–18 and became the fastest player to 10 goals in competition history.[30] He also joined Ronaldo,Lionel Messi andRobert Lewandowski as the only players to score in the double-digits for goals in the group stage.[31] On 23 February 2022, he made amends for an earlier own goal, and helped Ajax to a 2–2 away draw againstBenfica in the last, becoming the first player to score in seven consecutive matches in the competition;[32] his side lost 3–2 aggregate. With 21 league goals in 31 games, he finished theseason asEredivisie top scorer.[33]
On 6 July 2022, Haller signed a contract withBorussia Dortmund until 30 June 2026.[34] The transfer fee paid was€31 million, which could be increased to as much as €34.5 million after undisclosed bonuses.[35] However, on 18 July, the forward withdrew from the club's pre-season training camp in Switzerland, after he was diagnosed with amalignanttesticular tumour.[36][37] He then underwent twosurgeries and four cycles ofchemotherapy in order to control the spread of the disease.[38][39]
After successfully completing his treatments, in January 2023 Haller was officially allowed to return to full-time training, as he joined the rest of Dortmund's team at their winter camp inMarbella.[39][40] On 10 January, he played his first match in almost eight months, featuring in the final minutes of afriendly againstFortuna Düsseldorf.[39][41] Three days later, he scored a hat-trick within eight minutes in a 6–0 victory in another friendly againstBasel.[42] On 22 January, Haller came on as a second-half substitute in a 4–3 home win againstAugsburg, finally making his competitive debut for Dortmund after a 6-month battle with cancer.[43] On 4 February, he scored his first professional goal for the club in a 5–1 win againstFreiburg.[44] Haller missed a crucial penalty, when his team was trailing 1–0, during the final game of the2022–23 Bundesliga season which ended in a 2–2 draw withMainz. Borussia Dortmund subsequently suffered final-day heartbreak as they missed out on a first Bundesliga title for 11 years on goal difference.[45] In 2023–24, he sustained an ankle injury which sidelined him for most of the season, in which he only scored three goals including two againstTSV Schott Mainz in theDFB-Pokal and one againstAtlético Madrid in theChampions League quarter-final.[46]
On 30 August 2024, just before the transfer window closed, Haller joinedLa Liga clubLeganés on loan for the 2024–25 season.[47][48] However, the loan move ended early during the winter transfer window.[49]
On 9 January 2025, Haller rejoined his former club Utrecht on loan until the end of the season.[50] On 18 August 2025, he returned to Utrecht on a permanent basis with a one-season contract.[51]
On 14 November 2013, Haller made hisunder-21 debut, coming on forAnthony Martial in the 57th minute againstArmenia in a European qualifier inToulouse and scoring to conclude a 6–0 win.[54] He scored a hat-trick on 25 March 2015 in a friendly win of the same score againstEstonia,[55] and he did the same on 10 November 2016 in a 5–1 win over theIvory Coast at theStade Pierre Brisson.[56]
In December 2023, he was named in the Ivorian squad for the2023 Africa Cup of Nations hosted in his home nation.[61] In the semi-final match againstDR Congo, he scored the only goal in a 1–0 victory, which qualified his country to thefinal.[62] He later scored the winning goal in the final match againstNigeria which ended in a 2–1 victory.[63] However, ahead of the2025 Africa Cup of Nations in Morocco, Haller was ruled out of the tournament due to a hamstring injury sustained on 14 December 2025 while playing for his club, and was subsequently withdrawn from the Ivory Coast squad and replaced byEvann Guessand.[64]