On 6 May 2019, Leicester Tigers announced Lavanini's signing, with him set to join after the 2019 Rugby World Cup.[5] He made his Leicester debut from the bench on 2 November 2019 against Gloucester. He played 38 times for Leicester across two seasons, scoring two tries.
Lavanini was red-carded in the second test against South Africa in the 2017 Rugby Championship, following two yellow cards being issued to him. Lavanini made his return from suspension at home against New Zealand in Buenos Aires only to be yellow-carded for a dangerous tackle.[citation needed] He was red-carded for a high tackle on Owen Farrell in the pool game against England in the 2019 Rugby World Cup for which he received a four match ban.[10]
On 21 November 2021, against Ireland, Lavanini received a record-breaking third international red card, for a high tackle.[11] Lavanini is the most sin-binned rugby player in Argentina's history.[12]