Her father was Jang Han-pil, a county magistrate who lived in the western part of Chungcheong Province, and her mother was a concubine from the cheonmin class.
Because of this, Jang Nok-su lived as a servant of the Grand Prince Jean, son of Yejong of Joseon and Queen Ansun.
After having a son with Gano (가노; 家奴), another servant of Grand Prince Jean, she learned to sing and dance and became a kisaeng.
One day, Yeonsangun heard her voice and appointed Jang Nok-su his concubine, sending lots of gifts and wealth to her family.
Concubine Jang seemed to treat Yeonsangun as a baby, but he so favored her that all rulings and punishments were made under her influence.