Born in 1979 and raised in Porto Alegre, Brazil, Mario Reis grew up in the culturally rich Gaúcho region. His Brazilian Jiu-Jitsu journey began under the legendary Zé Mario Sperry, co-founder of Brazilian Top Team. Under Sperry's expert guidance, Reis rapidly progressed through the blue and purple belt ranks, quickly establishing himself as one of the sport's most promising talents.

Continuing his technical evolution, Mario Reis transitioned to the Winner-Behring team, training closely under renowned instructor Sylvio Behring. In 2003, Behring awarded Reis his black belt, marking the start of an exceptional competitive career. That same year, Reis made history by becoming the first black belt competitor to simultaneously win both the IBJJF World Championships and the CBJJO World Cup. His standout performances included impressive submission victories over elite athletes Fredson Paixao and Alexandre "Soca".

Mario Reis is celebrated for his aggressive, submission-oriented style, characterized by dynamic guard play and relentless attacking pressure. His tactical approach emphasizes constant offensive threats, fluid transitions, and precise submission setups. This distinctive style not only earned him considerable competitive success but also significantly shaped the technical mindset and competitive strategies of his students.

Following his retirement from active competition, Mario Reis fully embraced coaching, becoming the head instructor at Alliance Mario Reis academy in Porto Alegre. Under his leadership, the academy consistently ranks among the top affiliates globally in the AJP rankings. Reis has mentored numerous elite athletes, including BJJ superstar Nicholas Meregali, Fábio Alano, Lucas Gualberto, Gabriel Oliveira, and Jhonny Loureiro. Notably, Reis promoted Gabriel Oliveira to black belt in 2019, following Oliveira's victories at the IBJJF World and Pan Championships at the brown belt level.

Mario Reis maintains a strong international presence through regular seminars, instructional content, and active community engagement. His first European seminars took place in Spain and Holland in 2006, facilitated by his close friend Fabricio Werdum. Since then, Reis has expanded his global influence by establishing academies in England and Spain. He remains a highly sought-after instructor, frequently sharing his technical insights and competitive strategies through podcasts, interviews, and seminars worldwide.

In November 2019, Mario Reis faced significant backlash after excluding female athletes from his team's competition training sessions, with the sole exception of his ex-wife, Monique Ellias. In a leaked audio message, Reis explained the decision as being due to the high-intensity nature of the class. This decision sparked heated debates on Brazilian social media, drawing criticism from prominent figures such as Juliane Wiggers, a 2018 brown belt world champion and one of Reis's own black belts, who publicly accused him of misogyny. Other notable athletes, including Mahamed Aly, Luanna Alzuguir, and Ana Carolina Vieira, also extensively discussed the controversy.

Mario Reis is widely regarded as one of the greatest featherweight competitors in Brazilian Jiu-Jitsu history. His legacy extends beyond his competitive accolades, significantly influencing the sport through his dedicated coaching and mentorship. Alliance Mario Reis academy has become a flagship training center, consistently producing world-class talent and reflecting Reis's enduring impact on the next generation of BJJ athletes.