LaMotta was born in New York City, in the borough of the Bronx, near the Pelham Parkway and Morris Park area. He was forced by his father into fighting other children to entertain neighborhood adults, who threw pocket change into the ring. LaMotta's father collected the money and used it to help pay the rent.

In 1941, at the age of 19, LaMotta turned professional.

LaMotta, who compiled a record of 83 wins, 19 losses and four draws with 30 wins by way of knockout, was the first man to beat Sugar Ray Robinson, knocking him down in the first round of their first fight and then outpointing him over the course of 10 rounds during the second fight of their legendary six-bout rivalry.

On 14 November 1947, LaMotta was knocked out in four rounds by Billy Fox. Suspecting the fight was fixed, the New York State Athletic Commission withheld purses for the fight and suspended LaMotta. The fight with Fox would come back to haunt LaMotta later in life, during a hearing with the Federal Bureau of Investigation.

In his testimony and in his later book, LaMotta admitted to throwing the fight in order to gain favor with the Mafia. All involved agreed the fix was obvious and their staging inept. As LaMotta wrote,

The first round, a couple of belts to his head, and I see a glassy look coming over his eyes. Jesus Christ, a couple of jabs and he's going to fall down? I began to panic a little. I was supposed to be throwing a fight to this guy, and it looked like I was going to end up holding him on his feet ... By [the fourth round], if there was anybody in the Garden who didn't know what was happening, he must have been dead drunk."

The thrown fight and a payment of $20,000 to the Mafia got LaMotta his title bout against Marcel Cerdan.

LaMotta won the world title in 1949 in Detroit against Frenchman Marcel Cerdan, who was the world champion. Cerdan, called by many boxing critics the greatest champion ever from France,[citation needed] dislocated his arm in the first round and gave up before the start of the 10th. The official score had LaMotta as winner by a knockout in 10 rounds because the bell had already rung to begin that round when Cerdan announced he was quitting. A rematch was arranged, but while Cerdan was flying back to the United States to fight the rematch, his Air France Lockheed Constellation crashed in the Azores, killing everyone on board. LaMotta met two challengers (Tiberio Mitri and Laurent Dauthuille) and beat them, and then he was challenged by Robinson for their rivalry's sixth fight. Held on February 14, 1951, Saint Valentine's Day, the fight became known as boxing's version of the Saint Valentine's Day Massacre. Robinson won by a technical knockout in the 13th round, when the fight was stopped with LaMotta lying on the ropes.

In 1960, LaMotta was called to testify before a U.S. Senate sub-committee that was looking at underworld influence on boxing. He testified that he had thrown his bout with Billy Fox so that the mob would arrange a title bout for him.

In the mid-1950s, LaMotta suffered from a boxing injury and took time off to recover. He was always interested in baseball and decided to form the Jake LaMotta All-Star team. They played in Sterling Oval which was located between 165th and 164th Streets between Clay and Teller Avenue in the Bronx. He also held professional fights at that field, and his brother Joey often fought there.[citation needed]