Lee Sang-yi began his acting career in musicals before landing his first television appearance in the 2017 KBS2 series Manhole. In 2018 and 2019, he played supporting roles in JTBC’s The Third Charm and Special Inspector Labor Jo, respectively. He also became part of the top-rating KBS2 series When the Camellia Blooms, which took home the Daesang at the 56th Baeksang Arts Awards. His career breakthrough came in 2020 when he joined the KBS2 family drama Once Again, which won him Best New Actor at the KBS Drama Awards. He also received an Excellence Award at the 7th APAN Star Awards for his work in the series. In 2021, he bagged his first main role in the KBS2 period drama Youth of May, which earned him a Best Supporting Actor nomination at the KBS Drama Awards. That same year, he acted alongside Shin Mina and Kim Sun-ho in tvN’s Hometown Cha-Cha-Cha.

Lee Sang-yi graduated from Anyang Arts High School. He then studied acting at Korea National University of Arts.