is an Argentine professional footballer who plays as a midfielder for Premier League club Liverpool and the Argentina national team.

Mac Allister started his senior career with Argentinos Juniors in 2016, winning the 2016-17 Argentine Second Division in his debut season. He joined Brighton & Hove Albion in 2019 but was immediately loaned back to them until the end of the season and later to Boca Juniors, where he won the 2019–20 Primera División. Returning from the loan the following season, Mac Allister had his breakthrough year for Brighton, becoming a key player for the team, before moving to Liverpool in June 2023, where he won the 2023–24 EFL Cup and the 2024–25 Premier League titles.

Mac Allister represented Argentina at under-23 level, winning the 2020 CONMEBOL Pre-Olympic Tournament and playing at the 2020 Summer Olympics. He made his senior international debut in 2019 and was part of the Argentina squads that won the 2022 Finalissima, 2022 FIFA World Cup and 2024 Copa América.