Eoghan O'Flanagan was born on March 15, 1996, in London, England, and grew up in the North West area of the country. His relationship with martial arts began exceptionally early — before his toddler years were behind him, he was already practicing judo, competing in the sport regularly throughout childhood before stepping away at age 11.

At age 14, O'Flanagan set out to return to his old judo club, but a scheduling mix-up redirected the course of his athletic life. Arriving at the sports centre at the wrong time, he walked into a Brazilian Jiu-Jitsu class instead. Rather than leave, he joined in — and found the discipline immediately familiar. The ground-oriented problem-solving of BJJ echoed the judo he had grown up with, and he began training regularly from that point forward.

What started as three sessions per week escalated quickly. Within his first six months, O'Flanagan was training every day, blending BJJ sessions with continued judo practice. He maintained that demanding schedule from age 14 through 18, building the physical conditioning and technical depth that would serve him at every stage of his career.

O'Flanagan's formative BJJ training took place at New School BJJ in London, where he worked under Felipe de Souza, Rory Quarrier, Anthony Chahal, and Nicky Robinson. Of those instructors, Chahal and Robinson became his primary coaches, guiding him through the BJJ belt ranking system and shaping the technical foundation of his game.

At age 18, O'Flanagan relocated to Cardiff, Wales, to attend university. Over four years there, he trained under Craig Ewers, continuing his development away from his home gym before returning to New School BJJ in London after completing his studies.

On April 28, 2018, O'Flanagan was promoted to black belt at New School BJJ. Although Anthony Chahal and Nicky Robinson had shaped his game, the promotion was formally conducted by Helio Soneca, the association's team leader, who presided over the ceremony.

O'Flanagan's identity as a leg lock specialist traces back to a specific training context around 2015. At that time, Nicky Robinson was preparing for the ADCC Trials, and O'Flanagan became one of his primary sparring partners. The demands of no-gi preparation pushed O'Flanagan to research leg-locking techniques in earnest — a technical area he had not previously prioritized.

What began as a tactical adjustment in service of a training partner's preparation became the defining feature of O'Flanagan's own game. Heel hooks and leg locks evolved from a study subject into a competitive specialty, reshaping the entire direction of his career. Submission-oriented no-gi grappling became his primary focus, and his ability to threaten and finish with lower body attacks became the quality that set him apart on the international circuit.

O'Flanagan announced himself on the international stage in 2021, winning gold at the ADCC European Qualifier to earn a place at the ADCC World Championship — a result that confirmed what those within the UK no-gi scene had already recognized: that he was one of the country's most dangerous submission grapplers.

His performance at the 2022 ADCC World Championship elevated that reputation significantly. Competing in the 88kg division, O'Flanagan finished 4th overall, a run that included submissions of two of the tournament's favored competitors. The bracket showcased both his leg lock finishing ability and his capacity to perform under pressure at the sport's highest level. That 4th place finish at ADCC stands as the defining achievement of his competitive career.

O'Flanagan also claimed gold at GrappleFest in 2022 at 90kg and added an AIGA European Trials title in 2024, reinforcing his standing as a consistent and adaptable performer across formats and weight classes.

In June 2024, O'Flanagan announced he would compete in the Craig Jones Invitational, making a significant weight cut to drop into the under 80kg division. On August 16, 2024, he stepped onto the mat at Craig Jones Invitational 2024 and met Andrew Tackett in the first round. Tackett won via unanimous decision, with all three judges scoring the match 30-26 in his favor, ending O'Flanagan's run at the opening stage.

When the CJI 2 European trials were held in 2025, O'Flanagan did not compete. Craig Jones publicly addressed the absence in May 2025, revealing that a scheduling conflict had prevented O'Flanagan from taking part — closing the loop on speculation about why one of the UK's most prominent no-gi competitors had not appeared in the field.

New School BJJ has served as O'Flanagan's long-standing home base throughout his career, but in 2024 he took a more foundational step in shaping the UK no-gi landscape. That year, he co-founded Los Banditos Grappling Club alongside some of the region's top no-gi competitors, establishing a dedicated high-level training environment built around the submission-first culture he had spent his career developing.

Los Banditos represents O'Flanagan's primary competitive affiliation and stands as a direct expression of his investment in raising the standard of no-gi grappling in the United Kingdom.