Aarón Anselmino was born on 29 April 2005 in Bernardo Larroudé, Argentina, and joined the youth academy of Boca Juniors at the age of twelve. He signed his first professional contract with the club in June 2023 and made his senior debut the same day as a substitute in a 1–1 draw against Lanús, marking a swift rise through the ranks at one of Argentina's most storied clubs.
In August 2024, Chelsea secured his signature on a seven-year deal for a reported fee of £15.6 million, initially allowing him to remain at Boca Juniors on a twelve-month loan. After returning to Chelsea in January 2025, he made his debut for the club in June 2025, coming on as a late substitute in a 4–1 Club World Cup round-of-16 victory over Benfica — a tournament Chelsea ultimately won. He subsequently spent time on loan at Borussia Dortmund in the Bundesliga, where he scored his first senior goal in a 2–1 away win over Bayer Leverkusen in November 2025, before being recalled and then sent on loan to Ligue 1 side Strasbourg in February 2026.
A commanding central defender, Anselmino has been noted for his aerial ability and composure in one-on-one situations. Chelsea hold him as a long-term prospect, with his current loan at Strasbourg giving him regular first-team minutes as he continues his development.