Kim Ji Sook is the former main vocalist of the K-pop group Rainbow debuted on November 12, 2009 with the group’s first mini album Gossip Girl. She debuted as a member of Rainbow’s first sub-unit, Rainbow Pixie, on January 12, 2012 with the digital single "Hoi Hoi".
On October 28, 2016, DSP Media announced that Rainbow would be disbanding after 7 years of activities after all of the members decided not to renew their contracts with the agency.
On February 15, 2017, Starit Entertainment announced that she signed on with the agency.
She made her solo debut on May 22, 2018 with her first digital single "Umbrella".
In 2019, Rainbow reformed to celebrate their tenth-anniversary since debut with the special single album "Over the Rainbow".
On October 28, 2019, it was revealed that she has a relationship with computer programmer Lee Doo Hee. They married in a private ceremony held on October 31, 2020