Genk Trossard joined the
K.R.C. Genk youth academy from the
K. Bocholter V.V. academy in 2010. He was promoted to the senior squad in 2012, making his first, albeit brief, appearance on 13 May 2012 in a league match against
K.A.A. Gent. The game ended 3–1 in favour of
Gent. Trossard was introduced in the 87th minute, replacing
Stef Peeters. Those three minutes were the only ones he played in the league that season. For several seasons, he was consistently sent out on loan. As a result, he didn't score his first league goal for Genk until over four years later, coming in a 4–1 away loss to
K.V. Kortrijk on 25 September 2016. He was brought on as a substitute for
Leon Bailey and scored in the 63rd minute, assisted by
Bryan Heynen. In January 2013, Trossard was sent out on loan to
Lommel United. In twelve league appearances, he scored seven goals. His debut for Lommel came on 3 February 2013 in a 1–0 away loss to
Sint-Truiden. He was introduced as a substitute in the 63rd minute, coming on for Thomas Jutten. Arguably, the greatest game during his loan spell was his hat-trick in a 3–2 home victory over
K.F.C. Dessel Sport, in front of 2000 fans at the Soevereinstadion. He scored one in the 11th minute, another in the 60th (from the penalty spot), and the last in the 74th. He was subbed off in the 88th minute. In July 2013, Trossard was loaned out to
K.V.C. Westerlo. In 17 league appearances, he scored three goals. The first of these goals came on 9 August 2013 in a 2–0 away win over his former club
Lommel United. He scored in the 74th minute. He made his debut on 3 August 2013 in a 2–2 home draw with
A.F.C. Tubize. This was also his first start for the club. Trossard helped Westerlo to promotion to In July 2014, Trossard was loaned out to
Lommel United again. He continued his goal scoring form, finding the net 16 times in 33 league matches. He scored his second career hat-trick for Lommel on 22 March 2015 in a 6–0 demolition of
Racing Mechelen. His goals came in the 33rd, 61st, and 69th minutes. That season, Lommel were only nine points off promotion back to the top flight. In July 2015, Trossard was loaned out again, this time to
OH Leuven. In 30 league matches, he scored eight goals. He made his Leuven debut on 25 July 2015 in a 3–1 away loss to the club he had been loaned out from in
Genk. Genk didn't enforce the rule of not allowing loanees to play against them, as he was brought off the bench in the 61st minute, replacing
Yohan Croizet. His first league goal for Leuven came on 16 August 2015 in a 2–0 victory over
Charleroi. He made an immediate impact off the bench. He was brought on for
Yohan Croizet in the 82nd minute, and scored in the 85th.
Brighton and Hove Albion in 2022 On 26 June 2019,
Brighton & Hove Albion agreed to sign Trossard, who joined on a four-year deal with an option for an extra year, becoming the club's second signing of the summer, following
Matt Clarke's arrival from Portsmouth. Trossard made his debut on 17 August where he scored the equaliser in the 1–1 home draw against
West Ham United. Earlier in the game he was denied a goal for offside by
VAR. Trossard scored twice against
Norwich in the
2019–20 season, one in the 2–0 home victory on 2 November 2019, and again in a crucial 1–0 away win on 4 July 2020 to help Brighton push further away from the bottom three. On 31 January 2021, Trossard scored the only goal in a 1–0 home win over
Tottenham Hotspur to secure the Seagulls' first home league win of the
2020–21 season. Trossard played in Brighton's 1–0 away victory over defending champions
Liverpool on 3 February claiming their first league win at
Anfield since 1982, where he deflected
Steven Alzate's shot back onto Alzate, being awarded the assist in the only goal of the game. On 14 March 2021, Trossard scored the winner in a 2–1 away win over
Southampton, sealing Brighton's first win over the Saints in Premier League history. Trossard scored the first goal of Brighton's comeback from 2–0 down to beat champions
Manchester City 3–2 on 18 May, with fans returning to football. Trossard scored his first goal of the
2021–22 season on 11 September, firing in a 90th-minute winner scoring the only goal of the game in the 1–0 away win over Premier League newcomers
Brentford. He conceded a penalty by barging into
Conor Gallagher away at
Crystal Palace in the first
derby game of the season on 27 September, where
Wilfried Zaha converted the spot kick to take Palace 1–0 up at the break. However,
Neal Maupay scored a 95th-minute equaliser to take a point back to the south coast. Trossard scored Brighton's equaliser away at Liverpool on 30 October, completing a stirring fightback, coming from 2–0 down to earn a 2–2 draw. He enjoyed his time in North London in April 2022 by scoring two goals in two games against
Arsenal and Tottenham. Opening the scoreline in the 2–1 victory at Arsenal on the 9th and scoring a 90th-minute winner at the
Tottenham Hotspur Stadium on his 100th Albion appearance, seven days later. This was his sixth goal of the season, making it his best scoring season since joining the Sussex club. On 7 May, Trossard assisted two goals and scored one with his chest which had to be reviewed by VAR for potential handball in the 4–0 home thrashing of
Manchester United. Trossard scored his first goal of the
2022–23 season adding Brighton's second in the 2–0 away win at West Ham on 21 August, helping maintain their unbeaten run to 11 games against the "Hammers" in the Premier League. He scored his first home goal of the season on 4 September, putting Brighton back ahead in the eventual 5–2 home win over
Leicester City. In their next match on 1 October, Trossard became the first Brighton player to score a Premier League hat-trick in the 3–3 away draw at Liverpool. His first half double meant he was the first player to score two first-half goals at
Anfield since
Wigan Athletic's
Amr Zaki in October 2008. Trossard's hat-trick also meant he had scored four goals in two appearances at Anfield. In early January 2023, however, Trossard's relations with the club deteriorated sharply after manager
Roberto De Zerbi said he would drop the player for leaving a training session without permission. De Zerbi said he did not like the player's attitude or behaviour. In response, agent Josy Comhair accused De Zerbi of having humiliated the player in front of his team mates, saying a transfer was the best solution.
Arsenal 2022–23 season in 2023 On 20 January 2023,
Arsenal confirmed the signing of Trossard on a long-term contract. The fee consisted of a guaranteed £20 million, and around a further £7 million in add-ons. He was given the number 19 shirt by the club, and made his debut on 22 January as a substitute in a 3–2 win over
Manchester United. He made his full debut on 27 January against Manchester City in the
FA Cup fourth round. On 11 February 2023, Trossard came on as a substitute against Brentford and within four minutes scored his first goal for the club in a 1–1 draw. On 18 February, he was handed his first Premier League start for Arsenal in a 4–2 victory at
Villa Park. One week later, Trossard provided his first assist for the club in a 1–0 win at
Leicester City. He assisted all three of Arsenal's goals in their win at
Fulham on 12 March, becoming the first player in Premier League history to provide a hat-trick of assists in the first-half of a game, away from home and the first player since
Santi Cazorla to score a hat-trick and also register a hat-trick of assists in the same season. By the end of his first half-season with Arsenal, he had scored one goal and provided 10 assists.
2023–24 season On 6 August 2023, Trossard came off the bench and found the net in the final minutes of stoppage time to make it 1–1 against Manchester City in the
2023 FA Community Shield, forcing a
penalty shootout which Arsenal went on to win 4–1. On 17 September, he scored the only goal of the game in a 1–0 away win over
Everton, helping to seal Arsenal's first win at
Goodison Park since 2017. Three days later on 20 September, he scored his first
Champions League goal and provided an assist in a 4–0 win over
PSV Eindhoven on his debut in the competition. On 21 October, coming off the bench just after they scored a goal at the 78th minute, Trossard found the net at the 84th minute in a comeback against
Chelsea which finished 2–2. On 12 March 2024, Leandro Trossard scored the only goal in a 1–0 second leg win of the Champions League round of 16 tie against
FC Porto, taking the game to extra-time and penalties which Arsenal won 4–2, helping the Gunners progress to the quarter-final of the Champions League for the first time since 2009–10, ending a run of seven consecutive last 16 eliminations in the competition. On 6 April 2024, Trossard scored against his former club Brighton, scoring the third goal in a 3–0 away win that put Arsenal on top of the
Premier League table.
2025–26 season In the summer of 2025, Trossard signed a new contract with Arsenal, despite speculation about a potential departure from the club. Starting the season as an impact substitute, Trossard provided an assist in Arsenal’s 3–0 win against
Nottingham Forest and scored in the 2–0 Champions League win over
Athletic Bilbao. On 23 November, he scored and assisted in a 4–1
North London derby victory against Tottenham Hotspur. ==International career==