[6] Midthunder's mother Angelique, who is originally from Thailand and of Thai-Chinese ancestry,[7] is a casting director and stunt performer, and her father David is an actor of Hunkpapa Lakota, Sisseton Dakota, and Sahiyaiyeskabi Assiniboine descent;[8][9] Angelique and David met while working on the 1995 Japanese film East Meets West.

[10] Midthunder is a citizen of the Fort Peck Assiniboine and Sioux Tribe.

[11][12][13] She was born on the Navajo Nation in Shiprock, New Mexico, and eventually returned there after spending much of her childhood in Santa Fe where she attended the Academy for Technology and the Classics and where her mother worked in a casting firm.

[10][14] Midthunder developed an interest in acting as a child, where she would memorize and recite lines from her favorite shows, but disliked her first experience in the job,[15][16] leading her to take some time before another performance, even considering a career in make-up, where she worked as an intern, or mixed martial arts, having trained and taught Brazilian jiu-jitsu.

[14] Midthunder proceeded to work in various productions filmed in New Mexico, before moving to Los Angeles at the age of 17 to pursue more acting opportunities.