Barrett was born as Marlyne Nayokah Afflack in Brooklyn, New York. She began her career appearing on stage and television, before she co-starred with Hill Harper in the 2003 romantic comedy Love, Sex and Eating the Bones. Later in 2000s, Barrett had a number of guest starring television roles on the New York City-filmed dramas, include the NBC police procedural drama Law & Order and its spin-offs Law & Order: Special Victims Unit, Law & Order: Trial by Jury and the short-lived NBC legal drama Conviction. From 2006 to 2008, she played Nerese Campbell in the HBO crime drama The Wire, and in 2007 also had a recurring role as attorney Felicia Marquand in the FX legal drama Damages. In 2009, Barrett co-starred as Thomasina, the efficient palace secretary and aide-de-camp, on the short-lived NBC drama Kings.