Namajunas was born in Milwaukee, Wisconsin on (1992-06-29)June 29, 1992 to Lithuanian parents. She has said that her father suffered from schizophrenia, which led to complications and hardships during her youth. Namajunas started practicing Taekwondo at the age of 5. She earned her poom belt (junior black belt) at age 9. After that, she went on to practice both karate and jiu-jitsu. At the age of 16, while in high school, she started training in kickboxing and mixed martial arts with Duke Roufus at Roufusport, and she was also a senior-year wrestler at Milwaukee High School of the Arts.