Argentinos Juniors Like his two brothers, Mac Allister started his career with Club Social y Deportivo Parque before joining
Argentinos Juniors' youth setup. He made his
first-team debut on 30 October 2016, coming on as a second-half
substitute for
Iván Colman in a 0–0
Primera B Nacional home draw against
Central Córdoba. Mac Allister scored his first
goal on 10 March 2017, in a 2–1 away loss against
Instituto. He contributed with three goals in 23 appearances during
his first senior campaign, as his team achieved
promotion to
Primera División as champions. On 25 November 2017, Mac Allister and his two brothers all played together for the first time in a 1–0 loss at
San Lorenzo; Alexis and Francis were starters, while Kevin came on as a substitute. He scored his first goal in the top tier on 5 March 2018, with the opener in a 2–0 home win over
Boca Juniors.
Brighton & Hove Albion 2019–2020: Loans back to Argentina On 24 January 2019, Mac Allister signed for
Premier League club
Brighton & Hove Albion on a four-and-a-half-year contract. As part of the deal, Mac Allister was
loaned back to Argentinos Juniors for the remainder of the
2018–19 Premier League season. In June 2019, Boca Juniors completed the loan signing of Mac Allister, linking him up with brother Kevin, who had joined the club on loan six months prior. Mac Allister scored on his Boca debut, with the team's only goal in the first leg of a
Copa Libertadores round of sixteen victory over
Athletico Paranaense on 25 July.
2020–2022: Breakthrough and emergence Mac Allister made his debut for Brighton as an 80th-minute substitute in a 0–0 draw away to
Wolverhampton Wanderers on 7 March 2020. This match proved to be Brighton's last until the Premier League restart in June due to the
COVID-19 pandemic. Mac Allister played his first home game for Brighton where he came on as a substitute in a 2–1 victory over
Arsenal on 20 June. He made his first start for Brighton three days later, in a 0–0 draw away against
Leicester City, playing 58 minutes before being substituted. Mac Allister scored his first Brighton goal on 17 September 2020, with in a header in a 4–0 home victory over
Portsmouth in the
EFL Cup. He scored again six days later, this goal also coming in the EFL Cup where Brighton claimed a 2–0 away victory over
Preston North End. On 18 October, Mac Allister scored his first Premier League goal, a 90th-minute leveller, in a 1–1 away draw against bitter rivals
Crystal Palace. Mac Allister scored the winner and his second-ever Premier League goal as Brighton fought back from a goal behind to beat
Burnley 2–1 away on 14 August in the opening game of the
2021–22 season. He supplied
assists to both of
Aaron Connolly's goals on 22 September, in the 2–0 home victory over
Swansea City in the
EFL Cup third round. He later went off injured. Mac Allister scored his second goal of the season on 23 October, with an 81st-minute penalty in a 4–1 home defeat to
Manchester City. He scored his first
brace in a 3–2 away win over
Everton on 2 January 2022, putting Brighton 1–0 up in the third minute, and putting them 3–1 up in the 71st with a shot from the edge of the
penalty area. Mac Allister provided
Adam Webster's headed equaliser from a corner in a 1–1 home draw against the European champions,
Chelsea, on 18 January.
2022–2023: Club talisman and European qualification in 2022 In Brighton's opening game of the
2022–23 season against Manchester United, Mac Allister scored an own goal in a 2–1 victory that saw Brighton claim their first ever win at
Old Trafford. Two weeks later, Mac Allister scored from the penalty spot in the 2–0 away win over
West Ham United, and scored another penalty in a 2–1 defeat at
Fulham. Mac Allister scored a brace including a third penalty in four games after having a goal ruled out by
VAR in a 5–2 home win over Leicester City. On 24 October, Mac Allister signed a new contract, committing him to Brighton until at least June 2025, with an option for an additional year. Mac Allister returned after his World Cup victory on 4 January 2023 in a 4–1 away victory over Everton, where he came on as a substitute in the 62nd minute. On 7 January, he scored a brace in a 5–1 away win over
EFL Championship team
Middlesbrough in the third round of the
2022–23 FA Cup. On 14 January, his first return to Brighton's
Falmer Stadium since the World Cup, Mac Allister wore his winner's medal as he walked out onto the pitch ahead of the match against
Liverpool. Brighton went on to win the match 3–0. On 23 April, Brighton were eliminated from the
FA Cup in a 7–6
penalty shoot-out defeat to Manchester United. On 4 May, Mac Allister scored a 99th-minute penalty against Manchester United to win the game for Brighton. After the end of the
2022–23 season, in which Brighton finished 6th and qualified for the
UEFA Europa League and in which he was Brighton's top scorer with 10 goals, Mac Allister was heavily linked with a transfer to Liverpool. On 1 June, Mac Allister was voted as Brighton player of the season by users of
BBC Sport. He was shortlisted in the
UEFA Men's Player of the Year award for the season, coming in 10th after receiving 12 points in ranked voting.
Liverpool 2023–2024 season On 8 June 2023, Mac Allister signed for fellow Premier League club Liverpool on a five-year contract for an undisclosed transfer fee, reported to be an initial £35 million and a total of £55 million including add-on fees. On 13 August, he made his debut for the club in a 1–1 draw against
Chelsea in the Premier League. On 19 August, during a home match against
Bournemouth, Mac Allister received a
red card for a foul on
Ryan Christie which was criticised by analysts, opposition manager and fans. On 21 August, Liverpool announced their appeal and on 22 August the decision was successfully rescinded. On 24 September 2023, Mac Allister provided his first competitive assist for Liverpool with a long clipped ball for
Darwin Núñez in a 3–1 victory against
West Ham United. On 5 October, he shared the pitch with his brother Kevin after the former came on as a substitute in the 46th minute in a
Europa League group stage match against
Union Saint-Gilloise. Mac Allister scored his first goal for Liverpool on 3 December in a 4–3 win over
Fulham, with a shot 30 yards from the goal. The goal was voted the
Premier League Goal of the Month for December, and later
Liverpool's Goal of the Season for
2023–24. On 25 February, Mac Allister started in the
EFL Cup final and was substituted in the 87th minute before overtime in the 1–0 win over
Chelsea. He was named
Liverpool's Player of the Month for March with key contributions across competitions. On his time under manager
Jürgen Klopp's final season, Mac Allister added "I played as a lone five [holding midfielder]. I was much more defensive than anything else. We were used to being very direct and perhaps played more long balls."
2024–2025 season During the
2024–25 season, Mac Allister continued to be a consistent starting midfielder under new manager
Arne Slot. He made his
UEFA Champions League debut on 17 September, starting in a 3–1 away win against
Milan and scored his first goal in the competition against
Bologna on 2 October. On 27 November, Mac Allister scored the first goal and was named
man of the match in a 2–0 win over
Real Madrid, which was Liverpool's first victory against the Spanish club in 15 years. On 26 December, Mac Allister provided two assists for
Cody Gakpo and
Curtis Jones as his side came from behind to beat
Leicester City 3–1 in the
Premier League. On 27 April 2025, Mac Allister scored Liverpool's second goal in a 5–1 win over
Tottenham Hotspur that secured the club's second Premier League title and 20th overall English league title. He was later voted the
Premier League Player of the Month and
Liverpool's Player of the Month for April. and was also one of six nominees for the
PFA Players' Player of the Year. Mac Allister was also nominated in the 30-men shortlist for the
2025 Ballon d'Or finishing 22nd. On Mac Allister's position in the team, Slot added "My thought process is that [Mac Allister and
Gravenberch] are incredible [deep-lying midfielders in a 4–2–3–1 formation]. They're important to me but they're especially important to our attackers."
2025–2026 season in 2026 On 4 November, Mac Allister scored the winner and his first goal of the
season in a 1–0 win against
Real Madrid in the
UEFA Champions League. == International career ==