Siegel was friends with Meyer Lansky and Lucky Luciano, both of whom came up in the Mafia organizations with him. He became a bootlegger and was associated also to Albert Anastasia during the 1920s. Siegel was used for bootlegging operations in New York, New Jersey and Philadelphia.
Bugsy had been sent to California by mobsters to try to open a syndicate in the West. There, he became enamored with Hollywood star Virginia Hill and bought a mansion in Beverly Hills. On a return trip to the East, Siegel drove by the then small city of Las Vegas, in Nevada. Legend has it that, at the moment he had a vision of turning this city into a large gambling spot, he had stopped there to do a physical neccesity.
Bugsy had a vision where he would build large casinos and hotels where people could go and gamble. His vision was fueled by the fact Nevada had legalized gambling in 1931. Siegel returned to the East and convinced his fellow mobsters about the possibilities of building a major gambling mecca in Las Vegas.
After convincing his gangmates, Siegel returned and began working on his dream, with the construction of a casino he would name The Flamingo (nowadays the Flamingo Hilton Hotel). However, Siegel possessed little building knowledge, and it is rumored that the builders he hired stole thousands of dollars from him.
The Mafia members who invested in Siegel's project became worried back East, and they began suspecting Siegel was stealing money from them. In addition, Hill became a frequent visitor to Europe, and consequently, the gangsters started suspecting that Siegel was putting their money away in a Swiss bank account.
In 1946, several of his business and crime partners flew to Cuba for a meeting with Luciano, who had begun to operate Mafia operations from there after being paroled from jail in the United States. This meeting was kept a secret from Siegel, and they spoke about planning a hit on him. Lansky, who remembered fondly how Siegel had saved his life on various occasions when they were young, took a stand against the hit, and he asked them to give Siegel a chance until the casino opened. Luciano, who actually believed that Siegel could make a profit in Las Vegas and pay back what he owed the Mafia investors, decided to lay off the hit.
Siegel opened his casino on a star studded night, as many of Hollywood's luminaries showed up at the opening. But soon the casino ran dry of stars and customers, and the gangsters met once again, in Cuba, to decide whether they would liquidate Siegel. But to Siegel's luck, he had actually turned a profit on the month that the gangsters met for the second time, and Lansky stood up to object his killing once again. So Luciano decided to give him some time.
In 1947, Siegel married Hill in Mexico. The casino was, however, still losing money, and the Mafia decided they had given him too many chances to pay back the money he owed his investors. On June 20 of that year, Siegel was sitting inside the mansion he shared with Hill, when multiple shots were fired from outside, five of them hitting Siegel. The first shot ripped off his eye, which was found fifteen feet from the body.
He was interred in the Hollywood Memorial Park (now Hollywood Forever Memorial Park Cemetery) in Hollywood, California.
There have been different theories over the years about who actually killed Siegel, and a movie about his life, Bugsy, starring Warren Beatty as Siegel, was released in 1992.