On 28 August 2020, Tierney was in the starting 11 in the 2020 FA Community Shield, which Arsenal clinched a 5–4 victory over Liverpool in the penalty shootout after the match was 1–1 after 90 minutes. On 2 January 2021, Tierney scored the opening goal in a 4–0 away league win over West Bromwich Albion and later assisted the final goal, scored by Alexandre Lacazette. His stunning strike was subsequently voted the January Goal of the Month on the Arsenal official website. On 25 February, he scored a goal in a 3–2 win over Benfica in the Europa League round of 32, making him the first Scotsman to score for Arsenal in a European competition since Willie Young in March 1980. In June 2021, he signed a long-term contract with Arsenal.