Cynthia Kaye McWilliams was born in Berlin, Germany, but moved to United States, there raised primarily in Kansas City, Kansas. She graduated from the prestigious Theater School of DePaul University in Chicago, and later moved to Los Angeles, California. In 2005, McWilliams landed the recurring role as Kacee Franklin, C-Note's wife, in the Fox drama series, Prison Break. The following year, she appeared in film The Lake House, and later co-starred in the independent films Of Boys and Men and One Small Hitch.
In 2011, McWilliams co-starred in the short-lived Fox crime drama series, The Chicago Code as Lilly Beauchamp. She had a voice role as Misty Knight in the 2013 video game Marvel Heroes. In 2013, she began appearing in the recurring role of attorney Trina Shaw in the BET comedy series, Real Husbands of Hollywood. In 2015, after decade of playing supporting roles, McWilliams won the leading role in the NBC drama pilot, Love Is a Four Letter Word.
In 2015, McWilliams co-starred in the video game Halo 5: Guardians as Spartan Holly Tanaka.