Meghan Castellano was born and raised in the quintessential surf community of Oceanside, California. Her father was a respected Colonel in the United States Marine Corps who worked as a training officer. Her mother was a researcher at a nearby biotech company. From an early age, she was known as a high achiever in math and science and as an athletic prodigy. An Olympic hopeful in the 200-meter breaststroke, Castellano split her time between the pool and the army base. Her Olympic ambitions ended after she broke her arm in a car accident when she was sixteen.

She changed her focus after high school and enlisted in the United States Navy in the early 2000s. Castellano served four years before attending college on the Veterans Affairs bill. After graduating with a degree in Computer Science, specializing in Security and Cryptography, she transferred to the Navy's Information Dominance Corps. In 2007, Castellano collaborated with GROM Operator Elżbieta Bosak in Operation Orange Sky, acting as her source of intel.

Castellano's attention to detail and analytical skill made her one of the most sought-after specialists. She applied to become a SEAL when the position was opened to women and succeeded after several grueling years, acting as an encouragement for others to follow. During her training, she met Craig Jenson who served as an instructor for Hell Week. In 2016, Castellano accepted an offer to join Rainbow alongside Jenson.[2]

In 2019, Castellano and Twitch collaborated with Ghost Recon to conduct Operation Archangel in order to recover Caveira who had gone AWOL to Bolivia in order to search for her brother. While the mission was a success, it caused tensions to rise between her and Caveira.