Basilio began his professional boxing career by meeting Jimmy Evans on November 24 of 1948 in Binghampton, New York. He knocked Evans out in the third round, and five days later, he beat Bruce Walters in only one round. Although he started to box late in '48, he completed four bouts before the year was over.
He started 1949 with two draws, against Johnny Cummingham on January 5, and against Jay Perlin 20 days later. Basilio campainged exclusively inside the state of New York during his first 24 bouts, going 19-3-2 during that span. His first loss was at the hands of Connie Thies, who beat him by a decision in 6 on May 2 of '49. He and Cunningham had three more fights during that period, with Basilio winning by knockout in two on their second meeting, Cummingham by a decision in eight in their third, and Basilio by decision in eight in their fourth.
For fight number 25, it was decided that it was time to campaign out West. so Basilio went to New Orleans, where he boxed his next six figths. In his first bout there, he met Gaby Ferland, who held him to a draw. He and Farland had a rematch, Basilio winning by a knockout in the first round. He also boxed Guillermo Giminez there twice, first beating him by knockout in eight, and then by knockout in nine. In his last fight before returning home, he lost by a decision in 10 to Eddie Giosa.
For his next seven bouts, Basilio only went 3-3-1, but he was able to avenge his loss to Giosa by winning a ten round decision over him in Syracuse.
In 1952, Basilio went 6-2-1. He beat Jimmy Cousins among others that year, but he lost to Chuck Davies and Billy Graham (boxer). The draw he registered that year was against Davies in the first of the two meetings they held that year.
But things started to change in 1953. Basilio started winning big fights and soon found his name climbing up the Welterweight division's rankings. Soon, he found himself in his first world title fight, against Cuba's Kid Gavilan for Gavilan's world welterweight championship. Before fighting against Gavilan, he beat former world champion Ike Williams and had two more fights with Graham, avenging his earlier loss to Graham in the second bout between them with a 12 round decision win, and drawing in the third. Basilio lost a 15 round decision to Gavilan and went for a fourth meeting with Cummingham, this time winning by a knockout in four. Then, he and Pierre Langois began another rivalty, with a 10 round draw on the first bout between the two.
In 1954, Basilio went undefeated in eight bouts, going 7-0-1 with 2 knockouts, and defeating Langois in their rematch by decision.
1955 arrived and Basilio began by beating Peter Muller by decision. After that win, Basilio was once again the number one challenger, and on June 10 of that year, he received his second world title try, against world Welterweight champion Tony DeMarco. In what has become a favorite fight of classic sports channels such as ESPN classic, Basilio became world champion by knocking DeMarco out in the 12th. round. Basilio had two non title bouts, including a ten round decision win over Gil Turner, before he and DeMarco met again, this time with Basilio as the defending world champion. Their second fight had exactly the same result as their first bout: Basilio won by a knockout in 12.
For his next fight, in 1956, Basilio lost the title in Chicago to Johnny Saxton by a decision in 15. It has always been commented that the reason why Saxton got the nod that night was that he supposedly had ties with Chicago's underworld, which, according to the suggestion, might have paid off the fight's judges to give Saxton the fight. This has been an unveryfied rumor of which many magazines, Ring Magazine included, have talked about in the past. In an immediate rematch, which was boxed in Syracuse, Basilio regained the crown with a nine round knockout, and then, in a rubber match, Basilio kept the belt, by a knockout in two.
After that, he went up in weight, and challenged world Middleweight champion Sugar Ray Robinson, in what perhaps might have been his most famous fight. He conquered the Middleweight championship of the world by beating Robinson by a decision in 15 rounds, September 23, 1957. The day after, he had to abandon the Welterweigt belt, according to boxing laws. However, in 1958, he and Robinson met in a rematch on March 25 and Robinson regained the title with a 15 round decision.
From that moment, and until his retirement in 1961, he fought only sporadically, but 3 of his last fights were attempts to recover the world's Middleweight title, losing twice to Gene Fullmer; by a knockout in 14 at San Francisco; and by a knockout in 12, at Fullmer's home state of Utah (in Salt Lake City), and then also later, when he lost a 10 round decision to defending world champion Paul Pender.
In between those fights, he was able to beat former world champions Art Aragon, by knockout in eight, and Don Jordan, by decision in ten. His fight with Pender for the title, was also his last fight as a professionl boxer.
Basilio, who was also a member of the United States Marine Corps at one point of his life, was able to enjoy his retirement. During the 1970s, his nephew Billy Backus became world's welterweight champion after having a shaky start to his own boxing career, and Basilio declared on the day that Backus became champion, that to him, Billy winning the title was better than when he won it himself.
In 1990, Ed Brophy decided to build the International Boxing Hall Of Fame in Canastota, to honor the two world champions who were born there: Basilio and his nephew. Although Backus isn't a member of the Hall Of Fame, Basilio is, along with many of the fighters he met inside the ring.
In the late 1990s, Basilio's heart became seriously ill, and he required triple bypass heart surgery, but doctors were able to repair his heart, and nowadays, he continues working at the Hall Of Fame as a volunteer every day.
Basilio had a ring record of 56 wins, 16 losses and 7 draws, with 27 wins by knockout.