McCreary began her career acting in theatre, eventually making it to Broadway, and has performed in a number of productions by playwright Dominique Morisseau.

She appeared in several productions at the Minor Latham Playhouse, and worked on Columbia's Varsity Show during her junior year.

She also spent a semester at the British American Drama Academy in London and appeared in numerous commercials before graduating from Barnard in 2003.

However, she returned to performing when Dominique Morisseau's play Follow Me to Nellie's, which McCreary had previously workshopped, scored a production.

Her other stage credits include Secret Order with the Merrimack Repertory Theater, and A Midsummer Night's Dream and Eurydice with the Williamstown Theatre Festival.

[14] McCreary debuted in the penultimate episode of the medical drama's tenth season titled "Everything I Try to Do, Nothing Seems to Turn Out Right" in the role of Dr. Maggie Pierce, the half-sister of series protagonist Meredith Grey (Ellen Pompeo).

[20][21] In 2018, McCreary booked one of the lead roles in the Netflix animated series Harvey Street Kids, where she voices the character Dot.

[24] In 2018, McCreary also produced a short film titled A Cohort of Guests featuring several of her co-stars from Grey's Anatomy and Station 19, and reunited with Morisseau to star as Shanita in the Geffen Playhouse production of the playwright's Skeleton Crew.

While living in New York City, McCreary co-founded the Jaradoa Theater Company, an organization committed to community outreach.

The campaign aimed to increase voter turnout in the United States by encouraging citizens to register to vote in preparation for the upcoming midterm elections.

[25] In January 2019, McCreary revealed that she and director Pete Chatmon were engaged after meeting on the set of Grey's Anatomy two years prior.