Born and raised in California near the porn capital of the world, Martinez joined the industry in 2009. Like many performers, she began strictly as a girl/girl performer before branching out into boy/girl scenes. Though she felt a certain amount of anxiety as she went into her very first B/G shoot (with Calvin Calloway and MOFOS in I Know That Girl 7), she quickly found her groove. "I was really nervous! Then I realized ? hey, I've had sex before. I've got this!" Martinez told Adult Empire in a 2015 video interview. She soon became a frequent award nominee and fan favorite, known for her performances in Cherry Episode 2, Seduction Vol. 2, and many more.

Missy had several significant connections to Adult Empire over the latter half of her career. In 2015, she starred in an AE Films showcase movie entitled Fucked Ra, which spotlighted Missy in a Cleopatra-style theme. The movie was directed by Robby D. and featured a dazzling cover shoot from photographer Holly Randall, with contributions by noted makeup artist Melissa Murphy. ("I looked like a naked mole rat before, and afterwards, I looked like a sex goddess," Martinez said in tribute to Murphy's makeup talents.) The movie was Adult Empire's VOD bestseller for five straight weeks in autumn 2015, and it has since joined Scarlet Red and Villain as AE Films' all-time bestsellers. She also signed at Adult Empire's AVN booth in 2015, served as AE's correspondent at the 2016 AVN Entertainment Expo, and appeared in AE's 20th anniversary retrospectives.

Martinez's career has always been characterized by her loopy sense of humor. Her longtime Twitter bio jokingly mentioned that she was 80% sexy and 20% disgusting, an indication of her self-deprecating style. Her Twitter feed itself was and is filled with her tongue-in-cheek take on life and the industry. (Her pinned tweet is classic Missy: "Every scene I do is technically a DP because Jesus lives in my heart.")

In June 2019, she announced her retirement from the business, citing a desire to follow new pursuits.