Jackson Nagai was born on March 25, 1994, in Manés, Brazil, a region in the Amazon celebrated for its production of the açaí berry. At the age of 10, he relocated to Japan, where he initially channeled his athletic energy into basketball. A difficult family situation during his formative years redirected his development toward martial arts — first as a means of self-protection, then as a vehicle for personal discipline. He trained in karate and kickboxing before discovering Brazilian Jiu-Jitsu, the discipline that would ultimately define his competitive identity.

Jackson's younger brother, Samuel Nagai, followed a remarkably similar path. Samuel has since established himself as a prominent BJJ competitor with his own international accolades, making the Nagai family a recognizable name on the global grappling circuit.

Jackson Nagai's BJJ journey began at Evox BJJ in Japan under the instruction of Nori Toda. Seeking a higher level of competition and coaching, he later joined Nova União, where he trained under Marcio Pontes and earned his brown belt. That brown belt phase marked his emergence as a legitimate prospect on the international stage, with standout performances at IBJJF events and the Royal Invitational in the United States turning heads across the grappling community.

Among his most notable colored belt results, Nagai reached the final of the IBJJF World Championship as a brown belt in 2019 and claimed gold at the UAEJJF Grand Slam in Los Angeles at blue belt in 2015 — results that illustrated his consistent excellence across multiple belt levels. In January 2020, Lucas Leite of Checkmat awarded Nagai his black belt, formalizing a partnership that had brought him into the Checkmat system. Despite his Brazilian roots, Nagai competes internationally under the Japanese flag, representing the country where he came of age and forged his identity as a martial artist.

Jackson Nagai has built a reputation as one of the more versatile competitors on the IBJJF's global circuit, capable of performing at a high level across multiple weight divisions. His black belt career followed a clear upward trajectory: a runner-up finish at the 2020 IBJJF Pan Championship announced his arrival among the sport's elite, while bronze medals at the 2023 IBJJF World Championship and the 2023 IBJJF American Nationals — including an additional bronze in the absolute division at the latter event — demonstrated his consistency at the top of the division.

The 2024 competitive season represented the fullest expression of Nagai's capabilities. He claimed gold at the 2024 IBJJF Pan Championship in the 76 kg lightweight division, then returned later in the year to win the 2024 IBJJF World Championship in the 82 kg middleweight division. Capturing major IBJJF titles in two distinct weight categories within the same calendar year is a rare feat, demanding both technical adaptability and elite physical conditioning across a competitive weight range. That double gold placed Nagai firmly among the premier competitors of his generation on the sport's gi circuit.