Won Jin-ah made her acting debut in the 2015 film The Chosen: Forbidden Cave. In 2017, she landed the female lead role in the JTBC romantic melodrama Just Between Lovers, opposite Junho. Her work in the series won her Best New Actress at the 6th APAN Star Awards. She was also nominated for Best New Actress at the 54th Baeksang Arts Awards and the 2nd The Seoul Awards for her performance in the drama. In 2018, she acted alongside Lee Dong-wook and Jo Seung-woo in the JTBC medical drama Life. In 2020, she appeared in the film Long Live the King, which scored her a Best New Actress nomination at the 25th Chunsa Film Art Awards. In 2021, she became part of the main cast of the Netflix fantasy series Hellbound.

Won Jin-ah is the eldest child in her family. She has two younger brothers. She attended Hoseo University.