Macklemore and Ryan Lewis' song 'Same Love' features a woman singing the chorus. Who is she?

Her name is Mary Lambert, a Seattle based poet and singer. Lambert told the Seattle Times that she got a call from a friend  that was helping Macklemore and Ryan Lewis with their album. They needed a singer and a chorus for Same Love. She got a demo of the song and had a few hours to come up with something before going to the studio with Macklemore. She did and now it's changing her life.

Lambert's other work includes an album Letters Don't Talk, that came out in 2012 and a poetry book 500 Tips for Fat Girls.