Lee Si-woo started out as a model before making her acting debut in the 2021 JTBC fantasy mystery series Sisyphus. She was then cast as the female lead in the web drama Be My Boyfriend, opposite Shin Hyun-seung. In 2022, she played a rookie actress in the tvN romantic comedy Shooting Stars. That same year, she starred as one of the hostages in the Netflix series Money Heist: Korea – Joint Economic Area, which was based on the Spanish drama La Casa de Papel.