Early career After defecting to Germany in 2007, Romero made his professional mixed martial arts debut in December 2009. From 2008 to 2011, Romero was trained by Serge Kuftin (combat sambo & MMA coach) and Zike Simic (kickboxing coach), both of whom were from Peter Althof's "Martial Arts Gym Nürnberg". Over the three years, Romero amassed a record of 5–0 in various promotions in Germany and Poland. Romero won his debut via
TKO against Sascha Weinpolter. In his second bout, he scored a 62-second finish via
TKO against Ricky Pulu. He then took on Polish standout Michał Fijałka in his third bout. Romero won in the third round via TKO, which was at first ruled a controversial disqualification, due to a knee on the ground thrown by Romero. In 2011, he won his next three fights via TKO in the first round.
Strikeforce Romero signed with
Strikeforce in July 2011 and made his promotional debut against
Rafael Cavalcante on September 10, 2011, at
Strikeforce 36. He lost the fight via KO in the second round. A neck injury (a neck break to his C4 vertebra) kept him out of action until 2013.
Ultimate Fighting Championship 2013 After Strikeforce was purchased and absorbed by the UFC, Romero made his promotional and middleweight debut against
Clifford Starks on April 20, 2013, at
UFC on Fox 7. He won the fight via flying knee knockout in the first round. This win earned him
Knockout of the Night honors. Romero was expected to face
Derek Brunson on August 31, 2013, at
UFC 164. However, Brunson suffered an injury and pulled out of the bout. Promotional newcomer Brian Houston was briefly linked as a replacement, however Houston was not medically cleared to compete at the event and the bout was canceled. In his second UFC bout, Romero faced
Ronny Markes on November 6, 2013, at
UFC Fight Night 31. He won the fight via knockout in the third round.
2014 For his third fight, Romero was again set to face
Derek Brunson on January 15, 2014, at
UFC Fight Night 35. After trailing for two rounds, Romero won the fight in the third via TKO due to punches and elbows to Brunson's body. Both fighters earned a $50,000 a
Fight of the Night bonus award. In his fourth fight, Romero faced
Brad Tavares at
UFC on Fox 11. He won the fight via unanimous decision. Romero faced
Tim Kennedy on September 27, 2014, at
UFC 178. He won the fight via TKO in the third round, giving Kennedy his first stoppage loss in thirteen years. This fight generated much controversy: Romero was hurt badly at the end of round 2, and received extra time to recover between rounds. UFC color commentator
Joe Rogan mistakenly blamed this on Romero's cornermen for failing to leave the Octagon on time, when the blame was actually on a UFC
Cutman who applied too much Vaseline to a cut and referee
John McCarthy for allowing Romero to stay sitting while trying to get the cutman to return to the octagon to wipe the excess off. Later it was also noticed that Kennedy was illegally holding Romero's glove while striking him at end of round 2. The win earned Romero his second
Fight of the Night bonus award.
2015 Romero was expected to face
Ronaldo Souza on February 28, 2015, at
UFC 184. However, Souza pulled out of the fight on January 15, 2015, due to pneumonia. The bout was rescheduled for April 18, 2015, at
UFC on Fox 15. However, Romero was forced out of the fight by a ligament and meniscus tear in his knee. He was replaced by
Chris Camozzi. Romero faced former light heavyweight champion
Lyoto Machida on June 27, 2015, at
UFC Fight Night 70. This was the first UFC event, headlining Romero in the main event. He knocked out Machida at 1:38 of the third round with a series of elbows from top position. Romero was awarded a "
Performance of the Night" bonus. The bout with
Ronaldo Souza was scheduled for a third time, eventually taking place on December 12, 2015, at
UFC 194. Romero won the fight via split decision. 2 of 17 media outlets scored the bout in favor of Romero.
2016 Romero faced former middleweight champion
Chris Weidman on November 12, 2016, at
UFC 205. He won the fight via knockout in the third round and was awarded a
Performance of the Night bonus. It was announced that Romero was next-in-line for a title shot, after owning an 8-match winning streak.
2017 With middleweight champion
Michael Bisping sidelined due to injury, Romero fought
Robert Whittaker on July 8, 2017, at
UFC 213 for the interim UFC Middleweight Championship. Romero lost the fight by unanimous decision. This fight earned him another
Fight of the Night award.
2018 Romero was scheduled to face
David Branch on February 24, 2018, at
UFC on Fox 28. However, on January 13, 2018, it was reported that Whittaker had pulled out of his bout against
Luke Rockhold, which was scheduled to take place at
UFC 221, due to an undisclosed injury. It was announced he would be replaced by Romero in what was to be a fight for the interim UFC Middleweight Championship. The winner of this bout would then face Whittaker in a unification bout. At the weigh-ins, Romero came in at 188.3 lbs in his first attempt. He was given another two hours to make 185 lbs but failed to make weight, ending up 2.7 pounds over the middleweight limit of 185 lbs. As a result, Romero would not have been eligible for the interim championship had he won the fight. Romero was fined 30% of his purse, which was awarded to Rockhold. If Rockhold were to win, he would still be awarded the championship. Romero won the fight via KO in the third round. Romero knocked Rockhold down with a heavy overhand followed up with a punch on the ground that rendered Rockhold unconscious. A rematch with Whittaker took place on June 9, 2018, at
UFC 225. At the weight-ins, Romero missed weight, coming in at 186 pounds, 1 pound over the middleweight limit for a title fight. Romero was given additional time to make weight but was pulled by the commission, weighing in at 185.2 lbs, 0.2 pounds over. Romero was fined 20% of his fight purse and the fight proceeded as a non-title catchweight bout. Romero lost the back-and-forth fight by a close split decision. The fight was awarded as
Fight of the Night, but due to Romero missing weight, Whittaker received both $50,000 bonuses for a total of $100,000.
2019 Romero was scheduled to face
Paulo Costa on November 3, 2018, at
UFC 230. However, Romero indicated in mid-August that while he has been cleared to fight, his doctors have recommended that he wait another four to five months (early 2019) to allow facial injuries incurred during his most recent fight to fully heal. Romero was scheduled to face
Ronaldo Souza on April 27, 2019, at
UFC Fight Night 150. However, it was reported that Romero pulled out of the bout in early in April 2019 due to illness and was replaced by
Jack Hermansson. Romero faced
Paulo Costa on August 17, 2019, at
UFC 241. After trailing for the first two rounds, he dominated the third round in one of the greatest 3-round fights in the history of the
UFC. As he fell back in the numbers, he lost the fight via unanimous decision. This fight earned him the
Fight of the Night award.
2020 Romero next faced
Israel Adesanya on March 7, 2020
UFC 248 for the
UFC middleweight title. He lost the fight via unanimous decision. Many fans and pundits felt disappointed due to the low activity by both fighters, which resulted in a largely uneventful fight in which neither fighter was able to deliver any significant offense. Romero was scheduled to face
Uriah Hall on August 22, 2020, at
UFC on ESPN 15. However, Romero pulled out of the fight on August 11 for undisclosed reasons. The bout was subsequently cancelled. On December 4, Romero announced his departure from the UFC and became a free agent.
Bellator MMA On December 14, 2020, it was announced that Romero had agreed to a multi-fight deal with
Bellator MMA and was expected to compete in its
light heavyweight division beginning in 2021. On February 9, 2021, it was announced that Romero would be participating in the
Bellator Light Heavyweight World Grand Prix Tournament. He was scheduled to face
Anthony Johnson in the quarterfinal round at
Bellator 257 on April 16. On March 26, it was announced that the bout would be moved to
Bellator 258 on May 7. On April 29, it was announced that Yoel had failed his medicals due to an eye issue and the bout was pulled from the card, and the Grand Prix Tournament, being replaced by Jose Augusto. Romero made his Bellator debut on September 18, 2021, at
Bellator 266 against
Phil Davis. He lost the bout via split decision. Romero was scheduled to fight
Melvin Manhoef on May 6, 2022, at
Bellator 280. However, Manhoef withdrew from the bout due to a hand injury while stopping burglars and was replaced by Alex Polizzi. Yoel won the bout via TKO in the final seconds of the third round. The bout against
Melvin Manhoef was rescheduled this time for September 23, 2022, at
Bellator 285. Romero won the bout by knockout on the ground via elbows in the third round. Romero was scheduled to face
Vadim Nemkov for the
Bellator Light Heavyweight World Championship on February 4, 2023, at
Bellator 290. However, Nemkov was forced to withdraw due to undisclosed reason and the bout was scrapped. Romero faced
Vadim Nemkov for the
Bellator Light Heavyweight World Championship on June 16, 2023, at
Bellator 297. He lost the fight via unanimous decision. Romero faced
Thiago Santos on February 24, 2024, at
PFL vs. Bellator. He won the bout by unanimous decision.
Global Fight League On January 16, 2025, it was announced that he had left the promotion and signed with the Global Fight League. Romero was scheduled to face
Maurício Rua at a
to be announced date and location. However, Rua withdrew for unknown reasons and was replaced by former two-time
Bellator Middleweight World Champion Gegard Mousasi. In turn, all GFL events were cancelled indefinitely. ==Grappling career==