Romero made his professional debut on December 2, 2016, scoring a first-round technical knockout (TKO) victory against David Courtney at the Sam's Town Hotel and Gambling Hall in Sunrise Manor, Nevada.
[6] After compiling a record of 11–0 (10 KOs) Romero faced undefeated Dominican Jackson Maríñez for the vacant WBA interim lightweight title on August 15, 2020, at the Mohegan Sun Arena in Uncasville, Connecticut.
[13] The San Antonio crowd booed Romero as he was announced as the winner, voicing their displeasure with his roughhouse tactics of throwing elbows, shoving and grappling his opponent.
"[14] On October 6, 2021, it was announced that Romero would be facing undefeated WBA (Regular) lightweight champion Gervonta Davis on December 5 at the Staples Center in Los Angeles on Showtime PPV.
[17] On January 24, the WBA once again ordered Davis to make a mandatory lightweight title defense against Romero, and gave the pair until February 24 to come to terms.
[22] Puello was pulled from the fight on April 19, after testing positive for a performance-enhancing substance, and was replaced by Ismael Barroso who faced Romero for the vacant championship.
[27][28] Although Romero was ordered by the WBA to make a mandatory title defense against the twice-defeated Ohara Davies,[29] the pair failed to come to terms within the allotted 30-day negotiation period, which forced the sanctioning body to call for a purse bid to be held.
[32] On March 30, 2024 at T-Mobile Arena in Las Vegas, Romero was scheduled to make the first defense of his WBA light welterweight title against Isaac Cruz.