After suffering his first defeat against Olivares, Chacon won his next four bouts then faced off against cross-town rival and future champion Danny Lopez. Chacon outboxed Lopez and stopped him in the ninth round.
On July 9, 1974, Chacon won the vacant WBC Featherweight title by defeating former WBA Junior Lightweight champion Alfredo Marcano in nine rounds at the Grand Olympic Auditorium in Los Angeles. During his first period as a world champion, Chacon got to meet, and like, what many refer to as the sweet life. He became an alcoholic and he loved partying. His clashes with the law became matters of public knowledge, and his life went on a wild downward spiral.
Chacon lost his title in his second defense against arch-rival Ruben Olivares. Almost immediately after his loss against Olivares, he fought the first of his four fight rivalry with another world champion, Rafael Bazooka Limon. They would engage in what some boxing experts and historians have described as one of the fiercest and most spectacular boxing rivalries in history. Limon beat Chacon in their first bout by a decision.
Chacon then scored nine straight wins, leading him to a third match with Olivares. This time Chacon defeated Olivares in their 12 round bout by a decision. In Chacon's next fight, he lost an upset decision to Arturo Leon. Chacon rebounded by scoring victories over Ignacio Campos, Augie Pantellas, Gerald Hayes and Shig Fukuyama. He then fought to a technical draw in a rematch against Rafael Limon.
In 1980, Chacon had only one fight, but it was a significant one. He beat Limon in their third bout, and the WBC once again made him their number one challenger.
In 1981, Arguello had left the title vacant and gone up in weight to pursue the world's Lightweight title. Limon then beat Idelphonso Bethelmy by a knockout in 15 in Los Angeles to win the WBC world Jr. Lightweight championship. In his first title defense, he lost it by a decision to Uganda's Cornelius Boza Edwards, who, in turn, defended his title against Chacon on his first defense. In a televised bout, Edwards retained the world title by a knockout in the thirteenth round.
Chacon would go on to win five in a row in 1982, including a rematch victory over Arturo Leon, which kept him as the number one challenger, but then a dramatic development outside the ring would change his life forever: Chacon's wife, Valerie Chacon, flew to Hawaii on February of that year, hoping to convince him to leave boxing and move there if she found them good jobs. She was able to find a job, but unable to convince him to join her in Hawaii, so she flew back. She pleaded for him to leave the sport but wasn't able to convince him to do so, and one night before he boxed Salvador Ugalde, she grabbed a rifle and shot herself, dying instantly. Chacon went through with the fight and KO'ed Ugalde in the third round. He dedicated his win to his deceased wife.
Two more victories would follow, and then came his fourth and final bout with Limon. Limon had regained the world's Jr. Lightweight title by beating Rolando Navarrete by a knockout in 12 rounds. Navarrete, for his part, had won the title by beating Edwards by a knockout in five in Italy. Chacon-Limon IV became one of the fights of the year and the decade, according to such magazines as Ring Magazine, KO Magazine, and The Ring En Espanol, and Chacon recovered from knockdowns suffered in rounds three and 10 to drop Limon in the closing seconds of round 15, and secure a close decision and his second world title in Sacramento.
About one year and a half after Valerie's suicide, Chacon remarried and bought a large farm with a mansion and, according to what he said at an interview, about 40 horses. He also acquired a collection of Rolls Royce cars and some other vehicles. In between, he and Boza Edwards met for a second time, with his world title on the line, in what Ring Magazine called the fight of the year for 1983. Chacon rose from a knockdown in round one and recovered from a dangerous cut to drop Boza Edwards in round twelve and avenge his earlier defeat to the Ugandan former champion. He was then stripped of the world title for refusing to go to challenger Hector Camacho's home country of Puerto Rico to defend against him.
Chacon started 1984 with a move up in weight, to the Lightweight division, where he tried to join the exclusive club of boxing's three division world champions, but was knocked out in three during his challenge against world champion Ray Mancini in Reno. Chacon then beat Carlton Sparrow by a TKO in five rounds and announced his retirement.
Chacon came back in 1985 and he won five fights, including one against former world champion Arturo Frias by a knockout in seven, and a knockout in five over Rafael Solis , who had challenged Camacho for the world Jr. Lightweight title that had once belonged to Chacon.
In 1987 and 1989 he won one fight each year, and then he retired for good. But Chacon's life was once again marred by tragedy when his son was murdered in 1991. In 1996, he was spotted at a public appearance in Phoenix, Arizona to see the Pay Per View fight between Oscar de la Hoya and Julio César Chávez together with fans at a public fight viewing held at a plaza there. But by year 2000, he was living in a run down hotel, after having lost his mansion, his farm and his cars. He had, according to the hotel's manager, no way to pay the rent, so the manager fixed a small room with boxing equipment and a few photos of Chacon in his heyday so that he could train street kids there as a way of paying for the rent and to help Chacon remember who he is to boxing fans. Supposedly, Chacon and the manager later had trouble, so Chacon currently stays with his mother.
Chacon had a record of 59 wins, 7 losses and 1 no contest, with 47 wins coming by knockout. He holds victories over seven other men who held a world title. Olivares, Castillo, Lopez, Marcano, Limon, Edwards and Frias.
Some of his fights were broadcast by HBO's boxing show, HBO Boxing, and he was also able to beat Olivares (by a ten round decision in the third and final bout between them) and the then undefeated future world champion Danny Lopez, by a knockout in 9.
In January 2005, Chacon was elected into the International Boxing Hall of Fame. In December of that year, he, Mike Weaver and a group of lesser known former boxers from California held an autographs session before a boxing undercard in Los Angeles.
He is referenced in the Warren Zevon song "Boom Boom Mancini."