In 1987, Jordan Belfort (Leonardo DiCaprio) takes an entry-level job at a Wall Street brokerage firm. By the early 1990s, while still in his 20s, Belfort founds his own firm, Stratton Oakmont. Together with his trusted lieutenant (Jonah Hill) and a merry band of brokers, Belfort makes a huge fortune by defrauding wealthy investors out of millions. However, while Belfort and his cronies partake in a hedonistic brew of sex, drugs and thrills, the SEC and the FBI close in on his empire of excess.

The movie opens with a TV advertisement for Stratton Oakmont, Inc. It discusses the nature of Wall Street brokers, describing them as bulls or lions. A lion walks through one of the floors of the company.

We next see a large group of brokers playing a game where they throw little people onto a board with a dollar sign for a bulls-eye. Jordan Belfort (Leonardo DiCaprio) then introduces himself among those playing this game. He tells us that he is the son of two accountants living in Bayside, Queens. Ever since he started working on Wall Street, Jordan has enjoyed a life of endless drugs and countless hookers of his choosing. He is seen blowing cocaine into a hooker's butt, and then later flying a helicopter while hopped up on quaaludes. We also see him driving his Ferrari and getting a blowjob from a woman revealed to be his wife Naomi Lapaglia (Margot Robbie). According to Jordan, he does enough drugs to sedate the majority of New York's population. The one drug he loves the most, however, is the one that can make man conquer the world, and that is money. He snorts a line of coke with a $100 bill, crumples it up, and then tosses it in a wastebasket.

When he was 22 years old, Jordan began working on Wall Street while married to a woman named Teresa Petrillo (Cristin Milioti). He starts working as a broker and he meets his smooth-talking, easygoing boss Mark Hanna (Matthew McConaughey), along with another abrasive and foul-mouthed co-boss, Peter DeBlasio (Barry Rothbart). Jordan is astonished at how everybody talks and works. He has lunch with Mark, who is doing a rhythmic chant while pounding his chest. Mark orders enough martinis for them to "pass the fuck out". He asks Jordan how many times he jerks off: Jordan says about three or four times a week. Mark says those are rookie numbers and that he does it at least twice a day. He starts babbling to Jordan about how nobody knows if the stocks will go up, down, sideways, or whatever, and that it's all a "fugazi". Mark's primary reason for going into stocks was pretty much just for hookers and blow. He gets Jordan to join in the "Money Chant".

Jordan starts his first day with his broker's license on what happens to be October 19, 1987 - aka, Black Monday. The stocks around the world plummet, and Jordan loses his job. At home, Teresa suggests they pawn her engagement ring as he looks through the jobs section in the paper. He comes across one place in Long Island: "Investor Center" located in a small mini-shopping center.

Jordan shows up to Investor Center in a suit. The place is merely a small establishment that hardly looks professional, with most of the brokers dressing casually & the office being a dingy, unkempt workspace. Jordan is greeted by Dwayne (Spike Jonze), the man who runs the place. He assigns Jordan to pitch a sale for a company called Aerotyne, a small company out of a garage in Dubuque, Iowa. Aerotyne is also a "pink sheet" (low value) stock and he will receive 50% of the commission. Jordan calls a potential investor about Aerotyne. He sells it to him as a huge company (we're treated to a pic that shows it looking no bigger than a tool shed), but the way he pitches it draws everybody's attention. Everybody in the office stops what they're doing to listen to Jordan, who makes a very slick but also very professional sales pitch. He succeeds in making the sale and his new coworkers are impressed.

After a few months, Jordan is making serious money. He is approached in a diner by a chubby bespectacled man with fluorescent white teeth named Donnie Azoff (Jonah Hill). He asks Jordan if the Jaguar outside is his car, to which Jordan says 'yes'. Donnie says he lives in the same apartment building as Jordan and mentions he works selling children's furniture. He asks Jordan how much money he makes, and Jordan says he made $72,000 the previous month. Not believing it, Donnie asks to see a pay stub for $72,000. Jordan pulls one out, and Donnie calls his boss to tell him he's quitting to go into stocks.

Jordan and Donnie have drinks at a bar. We learn that Donnie married his cousin because he didn't like the idea of anybody else trying to sleep with her. Outside, Donnie smokes some crack and offers some to Jordan. He takes one hit and gets pumped, telling Donnie they need to go running.

The two find a garage where they plan to set up a business. Jordan recruits some of his friends to join. They include Robbie Feinberg (Brian Sacca; nicknamed "Pinhead"), Alden Kupferberg (Henry Zebrowski; nicknamed "Sea Otter"), Chester Ming (Kenneth Choi), Nicky Koskoff (PJ Byrne; nicknamed "Rugrat" because of his shoddy toupee), and Brad (Jon Bernthal). Brad is especially well known for making drug sales in his old neighborhood. Jordan tells Brad to sell him a pen that he pulls out of his pocket. Brad tells him to write something on a napkin. Jordan says he doesn't have a pen, and Brad "sells" it to him. Jordan also brings along several guys from Investor Center, including a guy called Toby Welch (Ethan Suplee).

Jordan and Donnie set up what is basically a boiler room in an abandoned auto garage. The guys are all set up at desks, ready to make calls with a script that Jordan wrote for them. They start with blue chip stocks like Disney and AT&T. Jordan calls one investor to purchase stocks in Kodak. Jordan anticipates closing the deal by making crude sexual gestures to everyone just as the investor signs on. From there, Jordan creates Stratton Oakmont and forms it into a much larger business with even more brokers working for him. He has groups of ambitious and hopeful brokers clamoring in his office showing off their resumes to his face. As one Strattonite makes a sale, the whole floor celebrates, with a marching band and a big group of hookers. They even have one female employee get her head shaved if Jordan pays her $10,000 for her to use for breast implants.