Welterweight Trinidad debuted as a professional on March 10, 1990, when he was 17 years old. The fight was against Angel Romero, another debuting boxer, in a contest that Trinidad won by knockout in the second round. At the beginning of his career, he knocked out nine of his first 10 opponents. on May 3, 1992, in
Cayey, Puerto Rico. This fight was the main event of the night. Both Gonzalez and Trinidad weighed in at 142 pounds. Gonzalez had a record of 8-2-3 with 5 KOs, while Trinidad had a record of 13–0 with 10 KOs. Gonzalez went down three times, and Trinidad took the victory in round four by TKO. Trinidad would add another victory by KO to his record and would now make it 14–0 with 11 KOs.
Welterweight title Trinidad traveled to
San Diego, California, and defeated the IBF welterweight champion
Maurice Blocker in two rounds, in a
fight card on June 19, 1993, televised by
Showtime. Trinidad spent the first two minutes of the fight analyzing Blocker's style. With 11 seconds left in the first round, one of Trinidad's punches injured Blocker, who barely survived the round. In the second round, the champion's condition improved, but after the first 30 seconds, another Trinidad punch injured him. Trinidad followed with a combination, scoring a knockout at 1:49 in the round when the referee stopped the fight. Afterward, tournament organizer
Don King's exclusive relationship to stage fights for the cable channel Showtime meant that Trinidad would be showcased regularly on Showtime Championship Boxing.
Trinidad vs. Camacho Trinidad defended his title for the next three years against several opponents. Trinidad's first fight in
Las Vegas was against
Héctor Camacho on January 29, 1994. He was cautious during the first rounds and received a cut over his left eye. In the third round he connected a solid combination that made Camacho change to a defensive stance. Throughout the fight Trinidad was on the offensive and won the fight by unanimous decision, in what was his first decision since he won the world championship. The scores awarded by the judges were 117–109, 116–110, and 119–106.
Trinidad vs. Campas On September 17, 1994, Trinidad traveled to the
MGM Grand for a second straight fight to compete in a title defense against
Yori Boy Campas, who had a record of 56–0. In the second round Campas scored a knockdown, the second knockdown in Trinidad's career. Following this Trinidad exchanged several combinations, injuring Campas' face and breaking his nose. In the fourth round, the referee stopped the fight, the first defeat in Campas' career.
Trinidad vs. Carr Trinidad's fourth fight outside Puerto Rico or the United States took place on
Estadio de Beisbol in
Monterrey, Mexico. Trinidad was scheduled to defend his title against the undefeated Oba Carr. In the second round, Carr scored a knockdown, which was the product of a quick right hand punch. Trinidad continued the fight and pursued the challenger, who displayed a quick pace throughout the fight. In the fourth round Trinidad connected a solid punch that injured Carr, and in the eighth he scored three consecutive knockdowns before the referee stopped the fight by technical knockout. Trinidad spent the next four years defending his title against numerous fighters in bouts televised on
Showtime. Among these fights was a defense against Mahenge Zulu, the number two challenger for Trinidad's championship. This fight was part of a card that took place on April 3, 1998, in
Bayamón, Puerto Rico and marked the first time that Trinidad had performed in the island in five years. The fight began with both boxers displaying aggressive styles, which included excessive pushing. In the following rounds both boxers used their jabs most of the time with Trinidad gaining an advantage when Whitaker attempted to attack inside, eventually scoring a knockdown in round two. The second round began with both boxers trading punches but De la Hoya quickly returned to his previous tactic, which he employed in the third round. In the second round Reid connected a solid punch to his opponent's jaw, and in the third round scored a knockdown. In the fourth and fifth rounds Trinidad used his jab consistently, gaining control of the fight's tempo in the sixth round. The fight began in a fast pace with Trinidad connecting a solid left hook that led to his opponent being knocked down. Vargas was able to stand up, but another classic left hook led to another knockdown. Early in the second round Trinidad was in the offensive but Vargas connected a solid combination at the round's closing moments which caused a slight swelling under Trinidad's right eye. Joppy opened the first round on the offensive, but late in the round Trinidad scored a knockdown with a combination of punches that came close to throwing Joppy underneath the ropes. In the second round, Hopkins connected some combinations, while Trinidad pursued the offensive in the fourth round and both boxers traded sequences of punches.
Next fight Trinidad was subsequently scheduled to fight against
Hacine Cherifi in a contest that he won by technical knockout in the fourth round. The event was part of a card that took place on May 11, 2002, and was organized in San Juan, Puerto Rico. Early in the first round Trinidad's strategy consisted of using his jab while Cherifi did not try to directly engage in the offensive.
Comeback Trinidad vs. Mayorga Trinidad announced a comeback on March 2, 2004. On October 2, 2004, he fought against
Ricardo Mayorga, in Madison Square Garden. Early in the first round Mayorga was on the offensive connecting several combinations, later in the round Trinidad connected some punches to his opponent's face. Mayorga reacted defiantly while lowering his defense, which Trinidad used to continue the offensive during the closing seconds. Trinidad's fighting style appeared to be out of rhythm in the first round, while Wright presented a defensive stance and relied on jabs.
Second comeback Trinidad vs. Jones Jr. Trinidad came out of his second retirement for a fight against former four-division champion
Roy Jones Jr. on January 19, 2008. According to the contract, it was contested at a
catchweight of , and was broadcast live on
HBO pay-per-view. The card took place at Madison Square Garden in New York City. Trinidad began the fight on the offensive and won the first two rounds. The third and fourth rounds were won by Jones who relied on the velocity of his punches. This pattern continued in the fifth and sixth rounds. During this timeframe, he made sporadic public appearances, attending boxing cards and participating in public activities, including a ceremony where
Juan Manuel López and
Iván Calderón received rings for five successful defenses of their world championships. Three months later, he was included in a storyline that also included
Orlando Colón. In 2010, Trinidad expressed interest in purchasing the
Changos de Naranjito. On September 12, 2018, judge Anthony Cuevas Ramos signed a letter which declared that the
Banco Popular de Puerto Rico must pay Trinidad $2,000,000 within 24 hours, due to them owing him interest money from his personal accounts at the bank. On February 13, 2023, the Trinidads reached a confidential agreement to solve their problems with their debtors, including Banco Popular de Puerto Rico, without going to court. ==Personal life==