Cassie became a recording artist unexpectedly. Shortly after being introduced to music producer, Ryan Leslie, her mother requested that Cassie record a song for her as a birthday gift. Cassie approached Ryan about producing the song, and Ryan put together a duet for them called "Kiss Me". As it turned out, Cassie's mother wasn't the only one who loved the song. Ryan played "Kiss Me" for Tommy Mottola, former chairman of Sony, and the record mogul behind the careers of Jennifer Lopez, Jessica Simpson, and most notably Mariah Carey. He offered Cassie a management deal, and weeks later she struck a deal with Ryan to produce her debut album. Cassie signed with P. Diddy's record label Bad Boy Recordings, after he heard her track "Me & U" played in a club.

Before the launch of her music career, Cassie was a fashion model for the Wilhelmina modelling agency, where she worked with Adidas, Complex magazine and Abercrombie & Fitch campaigns among others. As early in her modeling career as 2002 Cassie modeled for local department stores, the Delia's fashion catalogue and the popular magazine Seventeen.

In the months that followed, Cassie was invited on a promo tour to Germany for "Me & U", which had been leaked onto the internet and became a club hit. It quickly received nationwide attention from radio in the United States and was ranked #26 on the Rhythmic Top 40 chart. It also debuted at number 49 on the Pop 100 Airplay chart. The song became especially popular for its simplistic beat, which is matched by higher electronic tones. In May 2006, shortly after the single's release on the iTunes music service, "Me & U" rose and peaked at the #3 position on the iTunes Top 100 Downloaded Singles Chart, helping the single to rise to #6 on the Billboard Hot 100. ("SOS" by Rihanna kept it from #5 and thus from top five status) An interesting part of this success is the single rose to #6 with no official video released, a key part of promotion in today's music industry. As of July 15th (one week after the release of the video), Me & U has charted at #4 . The week after, the song advanced one place higher and has peaked at #3.

Her single "Me & U" has spawned three official urban remixes, the "YoungBlaze Remix" produced by and featuring rapper YoungBlaze, the "Ryan Leslie" produced remix, and the more recent "Bad Boy Remix" featuring Diddy and rapper Yung Joc. Un-official remixes of "Me & U" can be found on the internet with versions such as featuring Ray J, Juelz Santana, The Ying Yang Twins, 50 Cent, Ja Rule, Harry-O, and R. Kelly as well as several other clubmixes.

"Me & U" also has two videos - the older, lower budget video featured Cassie driving to a club, meeting a man, and taking him to an apartment. His face is not visible throughout, as it is filmed so the viewer is "in his shoes." It is extremely suggestive and leaked on to the internet not long after the release of the song, to the distress of Cassie (according to her myspace blog). A higher-budget video was later made featuring Cassie singing & dancing in front of a mirror in an otherwise empty room. On her blog, she stated that there was no man in this new video because it would seem "tacky." This music video is receiving heavy rotation on music video channels and programs, such as MTV and MTV2.

Cassie's next single, "Long Way 2 Go", is slated for a July release. Other songs that have been leaked include "Can't Do It Without U", "Miss Ur Touch" and "Just One Nite".