Early career

Muniz started his career travelling back and forth between his hometown and Rio de Janeiro, training with the likes of Thiago Santos and Luis Henrique at Tata Fight Team, and earning extra money on the side as a personal trainer to make ends meet in between fights. Starting off with a decision win over former PRIDE star and WEC middleweight champion Paulo Filho at the Bitetti Combat 19 event on February 6, 2014, Muniz would go on to win 10 out of the next 11 bouts between 2014 and 2018, culminating in being offered a chance on Dana White's Contender Series.^[7][8]

Dana White's Contender Series

Muniz was invited onto the Brazilian version of DWCS at Dana White's Contender Series Brazil 2 on August 11, 2018. He won a unanimous decision against Bruno Assis, but the win did not win him a UFC contract.^[9]

Almost a year later, Muniz returned to DWCS to face undefeated Taylor Johnson at Dana White's Contender Series 23 on August 6, 2019. He finished Johnson via rear-naked choke in the first round, finally winning a UFC contract.^[10]

Ultimate Fighting Championship

After two wins in Dana White's Contender Series, Muniz signed with the UFC and made his promotional debut against Antônio Arroyo at UFC Fight Night: Błachowicz vs. Jacaré on November 16, 2019. He won the fight via unanimous decision.^[11]

Muniz made his sophomore appearance against Bartosz Fabiński at UFC Fight Night: Overeem vs. Sakai on September 5, 2020. He won the fight via first-round armbar.^[12]

Muniz was scheduled to face Andrew Sanchez at UFC 257 on January 23, 2021.^[13] However, Muniz withdrew from the bout and was replaced by Makhmud Muradov.^[14]

Muniz faced multiple-time Jiu-Jitsu World Champion Ronaldo Souza at UFC 262 on May 15, 2021.^[15] He won the fight via technical submission in the first round after breaking Souza's arm in an armbar, becoming the first person to submit Souza in the process.^[16] The feat was widely recognized and named as the Submission of the Year by the mixed martial arts media and also the UFC itself.^{[17][18][19][20][21]}

Muniz was scheduled to face Dricus Du Plessis on December 11, 2021, at UFC 269.^[22] However, Du Plessis was removed from the event due to injury and he was replaced by Eryk Anders.^[23] He won the fight via an armbar submission in the first round.^[24]

Muniz was scheduled to face Uriah Hall on April 16, 2022, at UFC Fight Night 206^[25] However, Hall withdrew due to undisclosed reasons,^[26] and the bout was cancelled.^[27] The bout with Hall was rescheduled for UFC 276 on July 2.^[28] He won the bout via unanimous decision.^[29]

Muniz faced Brendan Allen on February 25, 2023, at UFC Fight Night 220.^[30] He lost the fight via a rear-naked choke submission in round three.^[31]

Muniz faced Paul Craig on July 22, 2023, at UFC Fight Night 224.^[32] He lost the fight via ground and pound TKO in the second round.^[33]

Muniz faced Park Jun-yong on December 9, 2023, at UFC Fight Night 233.^[34] He won the fight via split decision.^[35] 10 out of 14 media outlets scored the contest for Park.^[36]

Muniz was scheduled to face Ikram Aliskerov on June 15, 2024, at UFC Fight Night 242.^[37] However, the bout was cancelled because Muniz suffered a foot fracture which caused him to withdraw from the event.^[38]