Szalai started his career in his hometown ofBudapest, playing forBudapest Honvéd FC andÚjpest FC. In 2004, he moved to Germany to complete his development, spending two years at the youth academy ofVfB Stuttgart.
In hissecond season in theSegunda División B – the only tier in which he competed during his spell in Spain – he scored 16 goals in 37 games, but the side could only rank sixth, thus missing out onthe playoffs.[5]
Szalai scored his first goal for Mainz in a 1–0 home win overBorussia Dortmund on 10 April 2010.[8] He netted his second againstFC Bayern Munich on 25 September in a 2–1 away victory, with a powerful shot into the top corner in what was theRhineland-Palatinate club's sixth consecutive win ofthe season, in an eventual run of seven.[9] On 29 January 2011, at1. FC Kaiserslautern, the player sustained aknee injury –cruciate ligament – which sidelined him for the remainder of the campaign.[10]
On 22 January 2012, Szalai returned to action with Mainz after his injury, playing the second half of a 3–2 defeat at Leverkusen.[11] On 1 August he signed a contract extension with the club running until June 2015[12][13] and, on 27 October, scored his firsthat-trick for the team in a 3–0 home defeat ofTSG 1899 Hoffenheim.[14]
On 27 June 2013, Szalai signed a four-year contract with Schalke.[17] After making his official debut against amateursFC Nöttingen in thefirst round of theDFB-Pokal,[18] he played his first league match againstHamburger SV, scoring the hosts' last goal in a 3–3 draw after a shot fromChristian Clemens was poorly handled byRené Adler.[19]
Szalai was instrumental in helping his team reach the group stage of the Champions League. After a 1–1 draw in the first leg againstPAOK FC[20] he grabbed a brace in the second match inThessaloniki (3–2 win), and played the full 90 minutes on both occasions.[21]
On 3 July 2014, Szalai was transferred to Hoffenheim for €6 million. Sporting director Alexander Rosen said that he fitted into the club's style.[22] He made his debut for his new team against Augsburg, opened the scoring in a 2–0 home win[23] and was voted "Player of the Day" on the Bundesliga website.[24]
Szalai wassent off for the first time in his career on 22 November 2014 after committing a foul onDante in the 90th minute of the league fixture against Bayern Munich at theAllianz Arena,[25] being banned for two matches by theGerman Football Association.[26] On 12 December, he replacedAnthony Modeste at the hour-mark of a home game withEintracht Frankfurt; he scored the 2–2 equaliser three minutes later, and in the 87th he provided anassist with his ankle forRoberto Firmino's winner.[27]
On 4 January 2016, after being linked to a host of clubs,[28] Szalai continued in Germany by being loaned out toHannover 96 for the remainder ofthe campaign.[29]
On 27 August 2019, Szalai rejoined Mainz on afree transfer and a two-year contract.[30] Mainly a reserve in his second spell at theMewa Arena, he netted only four times in all competitions.[31]
On 29 February 2012, Szalai returned to the national team setup after his one-year injury with a goal againstBulgaria, in a friendly draw inGyőr.[41] On 7 September, in the nation's first2014 FIFA World Cupqualifier, he netted the third for the visitors in an eventual 5–0 win inAndorra.[42]
On 16 October 2012, Szalai helped hosts Hungary battle back to beatTurkey 3–1, scoring the second after an assist fromTamás Kádár.[43][44]
After an 8–1 defeat in theNetherlands for the 2014 World Cup qualification campaign, Szalai took part in a press conference where he gave poignant answers about what he thought the reasons behind the long-term underachievement of the national side were.[45][46] Subsequently, he found himself on the international wilderness.[47]
On 13 November 2013,Attila Pintér, manager ofHungarian League clubGyőri ETO FC, reacted to Szalai's statements and doubted his honesty. The coach claimed that the player said in an interview before the loss inAmsterdam that he did not have any problems with Hungary bossSándor Egervári, further disapproving of him for his irresponsibility of criticising the Hungarian coaches even though he did not know them.[48]
Hungary played its first match of 2014 on 5 March, and Szalai was left out. In an interview withNemzeti Sport, he said that he could not comment on his future with the national team since he was not invited and he did not have the option to decide whether to join or not.[49]
On 28 August 2014, Pintér selected his list for theEuro 2016 qualifier againstNorthern Ireland at theGroupama Arena on 7 September, and Szalai was not on it.[50] On 4 September, he posted an announcement on hisFacebook profile saying that he did not want to play for his country as long as Pintér was in charge,[51] and thus became the second Hungarian footballer in 20 years to renounce to the national side afterSzabolcs Huszti in 2007.[52]
On 18 September 2014,Pál Dárdai was appointed as Hungary's interim manager.[53][54] Eight days later, Szalai announced his return to the national team as the new coach stated the player was one of the side's "leading personalities".[55]
On 11 October 2014, Szalai marked his return by featuring the full 90 minutes inRomania in a 1–1 draw for the Euro 2016 qualifiers.[56] Three days later, in the same competition, he scored the game's only goal for an away win over theFaroe Islands inTórshavn.[57] After the victoriousqualifying play-off match againstNorway, he was recorded on video attending a bar in Budapest where fans were celebrating, and after giving a rousing speech about how they suffered the most during the unsuccessful period of Hungarian football, bought 200 shots ofpálinka for the people present;[58] the next day, he jokingly noted in a Facebook comment that he did not remember giving a speech.[59]
Szalai was selected for Hungary'sEuro 2016 squad.[60] He started and scored the opening goal in their first game in the tournament, a 2–0 defeat ofAustria inBordeaux[61] which marked his first after a 40-match dry spell that lasted over a year;[62] shortly before this happened, the Hungarian fans were chanting the name of fellow strikerDániel Böde, demanding a substitution.[63]
In October 2024, Szalai joinedMarco Rossi's coaching staff at the Hungarian national team.[68] His first game was a 1–1 home draw against the Netherlands in theNations League,[69] with playerZsolt Nagy having previously commented that Szalai's addition could be a motivating factor.[70]
In the first half of the reverse Nations League fixture against Netherlands on 16 November 2024, Szalai collapsed on the bench and was subsequently hospitalised.[71][72][73][74] The following day, as his condition had stabilised, he was released.[75][76]
On 16 October 2025, Szalai completed a international training course for national team players and obtained hisUEFA coaching licence.[77]