Sean Gismonte is an associate of the DiMeo crime family. He was Matthew Bevilaqua's partner in crime and an associate in the Soprano Crew . Sean and Matthew shared an apartment together. Sean's ambition was to impress his superiors in order to move up the ranks with his best friend, Matt. He is a cousin of Louis Gismonte, a convict who spent time in the license plate workshop with Richie Aprile. They worked under Christopher Moltisanti at a stock firm assigned to push Webistics, selling shares in the company to naive clients to pump the share price before Soprano Crew members dumped their shares for a profit. While at the brokerage they got into trouble with Chris for stealing other brokers' cars and beating a broker who sold other stocks. Led by Christopher, Matt and Sean broke several bank safes although they had to pay a large percentage of the cash to Tony. Matt and Sean also took part in the Soprano family's picket busting efforts at Massarone construction. Bevilaqua and Gismonte both tried to impress Tony in the Bada Bing restroom but angered him by speaking candidly about a "taste" of money they were giving him. Gismonte then blames Bevilaqua for making him do all the talking.
After these jobs, they felt they were getting nowhere under Christopher and decided they needed to take decisive action to move up in the ranks of the family. They planned a hit on Chris in order to get recognized by Richie Aprile, who they knew disliked Chris for striking his niece, Adriana, however it is revealed that Richie wouldn't have approved had he known. Matt and Sean pulled a drive-by hit as Chris left the Skyways Diner in Kearny. Sean shot Christopher multiple times but then Matt abruptly ran out of the car and Christopher retaliated. Sean attempted to follow Matt but his seatbelt was stuck and he could not escape. Christopher then fired off a shot that hit Sean in the head, killing him instantly.