Song Ji-eun debuted in the four-member girl group Secret with the single I Want You Back in 2009. The following year, they released their first mini album titled Secret Time, which produced their breakthrough song Magic. In 2011, Song Ji-eun recorded the non-album single Going Crazy, which became her first solo number one song on the Gaon Chart. In 2013, she released her debut solo single album Hope Torture. In 2014, she dropped her first solo extended play called 25, which was nominated for a Bonsang at the 2015 Seoul Music Awards.
Song Ji-eun made her acting debut in 2014 through the web drama Longing for Spring. In 2015, she led the cast of the KBS1 daily series Sweet Home, Sweet Honey, which earned her an Excellence Award nomination at the KBS Drama Awards. In 2017, she starred in the OCN rom-com My Secret Romance, opposite Sung Hoon. In 2019, she joined the cast of the tvN series Melting Me Softly.