On 1 July, Kovačić completed a permanent transfer to Chelsea, signing a five-year contract. After an underwhelming season under Maurizio Sarri, he turned into one of the most important Chelsea players under new coach Frank Lampard. Kovačić scored his first goal for Chelsea on 27 November, in a 2–2 Champions League draw against Valencia at Mestalla Stadium. On 7 December, he scored his first Premier League goal in a 1–3 away loss to Everton. In the 2020 FA Cup Final on 1 August 2020, he was controversially sent off for a rather soft challenge on Granit Xhaka, as Chelsea lost 2–1 to Arsenal. On 25 August, he was named the Chelsea Player of the Year.