Joshua James Emmett was born in Phoenix, Arizona and grew up near Sacramento, California. Emmett's original desire to train martial arts came from his desire to protect his mom, as Emmett grew up in a single parent household and saw police come to his home several times looking for his older brother. Emmett tried out kung fu as a child and began wrestling in middle school at the urging of his little league coach. Emmett continued wrestling at El Camino Fundamental High School in Arden-Arcade, California. Originally intending to join the United States Army, Emmett joined the Sacramento City College Panthers wrestling team after a phone call from Panthers coach Dave Pacheco. Emmett wrestled at City College from 2003-2005, before transferring to Menlo College in Atherton, California. Emmett graduated from Menlo in 2010 with a degree in Psychology. Emmett also began competing in no-gi Brazilian jiu-jitsu and is a purple belt in BJJ. Emmett owned a CrossFit gym and worked as a personal trainer between 2013 and 2017.

Emmett began training with Urijiah Faber in 2006 and made his MMA debut in 2011. Emmett traveled the California regional scene and went 9-0 to start his MMA career. He won the West Coast FC Lightweight Championship over Brandon Ricetti (West Coast FC 12) and defeated future UFC Lightweight Christos Giagos to win the ISCF Pro California Lightweight Championship (West Coast FC 16).

Emmett made his UFC debut on May 8, 2016 at UFC Fight Night: Overeem vs. Arlovski. He went 2-1 as a Lightweight before moving down to Featherweight. Emmett won his first two Featherweight fights against Felipe Arantes (UFC Fight Night: Cowboy vs. Till)(unanimous decision) and Ricardo Lamas (UFC on Fox: Lawler vs. dos Anjos)(KO) before being knocked out by Jeremy "Lil Heathen" Stephens (UFC on Fox: Emmett vs. Stephens). 

Emmett has been 5-0 since then and has been climbing up the Featherweight Division. He defeated Michael Johnson (UFC on ESPN: Barboza vs. Gaethje) and Mirsad Bektic (UFC Fight Night: de Randamie vs. Ladd) by KO/TKO before winning three straight decision victories over Shane Burgos (UFC on ESPN: Blaydes vs. Volkov), Dan Ige (UFC 269), and former Featherweight title challenger Calvin Kattar (UFC on ESPN: Kattar vs. Emmett). The Kattar win immediately sparked controversy and has been heavily dissected by fans and media since. The early rounds were fairly close, but Kattar outstruck Emmett in the championship rounds, thwarted his takedowns, and had Emmett's left eye swollen shut. Nevertheless, Sal D'Amato and Chris Lee gave Emmett the 48-47 nod (Douglas Crosby had it 48-47 Kattar). Emmett's TKO victory over Bektic won him Performance of the Night Honors, while his victories over Burgos and Kattar won him Fight of the Night Honors. As of 9/1/2022, Emmett is tied with Bryce Mitchell for the fourth longest win streak among Top 15 UFC Featherweights with five consecutive wins (following Alexander Volkanovski's twelve, Arnold Allen's nine, and Movsar Evloev's six). 

Emmett has been campaigning for a title shot at Featherweight since his win over Kattar. As of 9/1/2022, Emmett is the #4 Featherweight in the UFC. Emmett lives with his wife in Sacramento and trains at Team Alpha Male.