She is known for playing Emma Pillsbury in the Fox musical series Glee (2009–2015) and for her starring roles in the films Red Eye (2005), Paul Blart: Mall Cop (2009) and The Smurfs (2011).

Mays' other credits include Six Feet Under, Stacked, How I Met Your Mother, Heroes, Pushing Daisies, The Comeback, Entourage, Ghost Whisperer, and Ugly Betty.

From 2017 to 2018, Mays starred in the NBC crime anthology comedy Trial & Error as prosecutor Carol Anne Keane.

She also appeared in a 2018 episode of Great News as Cat, the girlfriend of Greg, played by Mays's husband Adam Campbell.

In April 2021, it was announced that Mays was cast in Disenchanted, the long-awaited sequel to the 2007 film Enchanted, along with Maya Rudolph and Yvette Nicole Brown.