She began her career as a result of meeting record producer Ryan Leslie after moving to New York City, who signed her to his NextSelection imprint. They later convinced P. Diddy to partner Bad Boy Records with them for the release of her debut album.
Her self-titled debut album Cassie was released in August 2006, preceded by the single "Me & U" which became a major worldwide hit. She began work on her sophomore studio album in following years, having released various standalone singles since then. Throughout the decade that followed and with her follow-up project slated and shelved twice, Cassie developed a cult following and has been credited as one of the pioneers of "experimental R&B" due to her distinct "icy" sound. In April 2013, Cassie released her debut mixtape RockaByeBaby to positive reception.
Apart from music, Cassie is signed to modeling agency One Management and has featured in several magazines and ad campaigns. Cassie also ventured into acting in 2008, making her film debut in Step Up 2: The Streets. Cassie is known for being a style icon due to her "edgy style" and "feminine" and "sophisticated" fashion. She popularized the trend among women of half-shaving their head, after shocking fans and partially shaving her hair in 2009.