Seo Hyun-jin debuted as the main vocalist of the South Korean girl group M.I.L.K. They released their first and only album With Freshness in December 2001. In 2002, they were nominated for Best New Group at the 2002 Mnet Music Video Festival for the song Come to Me. The group disbanded in 2003 following the departure of one of its members, Bae Yu-mi.

Seo Hyun-jin made her acting debut in 2006 in the musical The Sound of Music. In 2011, she was named Best New Actress at the MBC Drama Awards for her work in the sageuk The Duo. In 2012, she bagged an Excellence Award at the MBC Drama Awards for her performance in the dramas Feast of the Gods and Oh Ja-ryong Is Coming. Her popularity surged to new heights when she starred the 2016 tvN series Oh Hae-young Again, which won her the Best Actress trophy at the 53rd Baeksang Arts Awards. This was followed by a leading role in the 2016 SBS series Romantic Doctor, Teacher Kim, in which she received an Excellence Award at the SBS Drama Awards.  In 2017, she was hailed Best Actress at the 30th Grimae Awards for the SBS drama Temperature of Love.

Seo Hyun-jin majored in applied musicology at the Dongduk Women’s University.