2017: GOOD DAY, The Unit
On July 10, 2017, she was announced as a member of C9 Entertainment's newest girl group GOOD DAY. They debuted on August 30, 2017, with their first mini album All Day Good Day.
Later that year, she became a contestant on KBS 2TV's reality survival show The Unit. She was eliminated in the episode 15 after ranking 11th place, as only the final 9 made it into the final lineup.
On November 10, 2019, Jee Won was introduced as the first member of C9 Entertainment's next girl group, Cignature. They debuted on February 4, 2020 with the digital single "Nun Nu Nan Na", now managed by the subsidiary J9 Entertainment.