Martinez started working in the comics industry in the 1990s as an assistant to Joe Quesada on Azrael & Ash and Daredevil, then as an inker’s assistant on Aquaman. She got her first headlining role as artist on Iron Man, then moved on to X-men: Black Sun, Marvel Age Fantastic Four, Black Panther and Voltron.
In addition to her creator-owned work Yume and Ever, she illustrated three graphic novels for younger readers and teens for Graphic Universe: Kung Fu Masters, written by Evonne Tsang; The Quest for Dragon Mountain, written by Robin Mayhall; and My Boyfriend is a Monster #3: My Boyfriend Bites, written by Dan Jolley. Her former Iron Man editor Bobbie Chase brought her on as an artist on the Gail Simone-scripted Batgirl series in 2012. After Batgirl, she began work on New Crusaders from Archie Comics.