Martin-Green was born in Russellville, Alabama. She has one sister and three older half-sisters. She had initially planned to become a psychologist before deciding to pursue a career in acting when she was in the tenth grade.On her decision to become an actor, she said, “I didn’t know I was going to be an actor until I was 16. I thought I was going to be a psychologist, which is interesting because it’s very similar to acting. I was fascinated with human behavior and why people do what they do. I was in the middle of rehearsal in 10th grade when I had this epiphany. And so I got my theater degree from the University of Alabama.”
She is best known for her television role as Sasha Williams on The Walking Dead, a role she played from 2012 to 2017. Before that, she had starred in several independent films before gaining her first recurring role as Courtney Wells on The Good Wife. Later, she had recurring roles as Tamara in Once Upon a Time and Rhonda in New Girl. She currently plays the lead role as Michael Burnham in the web television series Star Trek: Discovery.