Matheus Diniz was born on April 8, 1993, in Uberlandia, Minas Gerais, Brazil. At a young age, he relocated to Formiga, Minas Gerais, notably the hometown of legendary grappler Marcelo Garcia. His martial arts journey began at age 10 with capoeira, though his training was interrupted when behavioral issues led to his expulsion from school.

Diniz first encountered Brazilian Jiu-Jitsu at age 15, initially driven by a personal conflict with a local practitioner. Visiting the rival's academy intending confrontation, Matheus instead met instructor Rodrigo Ranieri, who defused the situation and encouraged him to channel his energy into training. Under Ranieri's mentorship, Diniz quickly embraced the discipline, earning his blue belt and demonstrating notable talent and dedication.

Seeking higher-level training and competition opportunities, Matheus moved to Poços de Caldas to train full-time at Paulo Rezende's academy. Under Rezende's guidance, he rapidly progressed, earning his purple and brown belts while achieving significant competitive success. During this period, Diniz connected with Marcelo Garcia, who recognized his potential and provided financial support for competitions. Impressed by Matheus' dedication and skill, Marcelo invited him to train at his renowned academy in New York City. In April 2015, Marcelo Garcia awarded Matheus Diniz his black belt.

Matheus Diniz reached the pinnacle of submission grappling by winning the 2019 ADCC World Championship. Returning to defend his title at ADCC 2022, he advanced to the second round before being eliminated by Giancarlo Bodoni, who went on to win the 88 kg division.

Following Marcelo Garcia's semi-retirement, Matheus Diniz assumed the role of head instructor at Marcelo Garcia's academy in New York City. In this leadership position, he directs training sessions, mentors competitors, and maintains the academy's prestigious competitive legacy.

In mid-2024, Diniz made headlines by declining his invitation to ADCC 2024 in favor of competing at the inaugural Craig Jones Invitational (CJI), attracted by its unprecedented $1 million prize pool. To compete in the 80 kg division, Diniz undertook a significant weight cut, dropping from approximately 225 lbs early in 2024 down to the 173 lbs limit. At the August 2024 CJI in Las Vegas, his campaign ended in the quarter-finals when he was submitted by Kade Ruotolo via straight ankle lock.

Matheus Diniz is widely recognized for his aggressive, pressure-oriented grappling style. His tactical approach emphasizes relentless guard passing, dominant positional control, and adaptability across multiple weight divisions. Known for his physical intensity and technical versatility, Diniz consistently applies strategic pressure to neutralize opponents, making him a formidable competitor in both gi and no-gi formats.