Following injuries to Sead Kolašinac and Kieran Tierney, Saka began to establish himself as a regular in the Arsenal first team at left-back. On 27 January 2020, he scored the opening goal in Arsenal's 2–1 FA Cup fourth round victory at Bournemouth after finishing a 22-pass move, as well as assisting the second goal, scored by Eddie Nketiah. The goal was later voted goal of the round by the BBC. After a two-week mid-season break, Saka marked his return to action at home to Newcastle United with an assist for Nicolas Pépé's goal. He then set up Alexandre Lacazette for his ninth assist of the season in a 1–0 win at Olympiacos in the UEFA Europa League. He then hit double figures for assists that season after crossing in for Nketiah in a thrilling 3–2 home win against Everton. Further performances against Portsmouth and West Ham United further strengthened his grip in the first team.
On 1 July 2020, Saka signed a new long-term contract with Arsenal. Head coach Mikel Arteta praised Saka and said: "I think he represents every value that this football club stands for. He has come through the academy, and earned his respect with hard work and accountability and you can see the progression that he is having as a player but as well as a person." He scored his first Premier League goal for the club against Wolverhampton Wanderers, with a half volley beating goalkeeper Rui Patrício, in a 2–0 win. Saka was an unused substitute as Arsenal defeated Chelsea 2–1 to win their 14th FA Cup.
On 4 September 2020, Saka made his debut for England U21s during a 6–0 victory away to Kosovo.
On 1 October 2020, Saka was called up to the England senior squad for the first time, and made his international debut as one of the starters in a 3–0 victory over Wales.