Lenny Cole (Tom Wilkinson) is a crime boss who calls the shots in London's underworld and real estate market. Lenny and his methods of acquisition are explained by Archy (Mark Strong), his second in command who serves as the film's narrator. The main characters are introduced in Archy's opening voiceover. A billionaire Russian businessman, Uri Omovich (Karel Roden), plans a crooked land deal, and London's crooks all want a piece of it. Other key players include the underhand accountant Stella (Thandie Newton) and ambitious small-time crook One-Two (Gerard Butler).

When the wealthy Uri Omovich looks to Lenny for help on a major new deal, Lenny is eager to assist for a large fee. Uri agrees to pay, and as a show of faith, he insists that Lenny borrow his “lucky” painting. Uri then asks his accountant, Stella, to transfer the money to Lenny, but things quickly go awry when a band of thieves known as “The Wild Bunch” intercept the money before it reaches him (at the behest of Stella). Wild Bunch members Mumbles and One-Two see the heist as an opportunity to pay Lenny back a huge sum of money owed to him. Lenny had given them a loan to buy a building and then ordered the local Councillor to deny their petition, knowing the property would kick back to him. However, they are unaware that they are stealing from both Lenny and the Russian mob. Also unknown to them is the fact hat the lucky painting has mysteriously been stolen, and the number one suspect is Lenny's estranged stepson, crack-addicted rock star Johnny Quid (Toby Kebbell), who is presumed dead. As Lenny desperately tries to locate the painting, Uri calls in his henchmen to recover his money.

In an attempt to find Johnny, Lenny and Archy enlist his record producers Mickey (Chris Bridges) and Roman (Jeremy Piven) to track him down. In order to gain leverage over them Cole's men make it clear that their concerts and clubs will be shut down if they do not comply.

Uri makes a decision regarding Stella, whom he has been smitten with for a long time. He arrives at Stella's house to seal their arrangements while also asking her to marry him, but spots his lucky painting in Stella's living room. On being asked how long she's had it, Stella says she's had it for years, not knowing it's actually Uri's. It is implied that she is murdered.

Meanwhile, Archy brings Johnny, the Wild Bunch, Mickey and Roman to Lenny's warehouse where Johnny begins to verbally provoke his crippled stepfather. Lenny then shoots Johnny in the stomach before he can finish what he says. Lenny then orders Johnny, Roman and Mickey be brought downstairs and executed. He then angrily demands that the Wild Bunch tell him where Uri's money is. Handsome Bob calls out to Archy and offers the documents in his jacket pocket which reveals that the “rat” in the ranks, codenamed “Sidney Shaw”, was Lenny all along. Lenny arranged with the police to routinely throw many of his associates in prison for years at a time in order to secure his own freedom and sow fear among his gang. One Two, Mumbles and even Archy are among the people Lenny has informed on over the years. With the information brought to light, Archy orders Lenny's men to free the Wild Bunch and oversees Lenny's execution by drowning.

Johnny informs Mickey and Roman how they will be executed, prompting Lenny's man to move prematurely. Mickey and Roman intervene and kill their presumed exectuioner. Johnny shoots two more men waiting at the top of the elevator. They overcome the last of the gangsters and escape.

Later, Archy picks up a rehabilitated but still eccentric Johnny Quid from the hospital. Archy offers Uri's lucky painting to Johnny as a peace offering and “welcome home present”, which Johnny happily accepts. Archy reveals to Johnny that obtaining the painting “cost a very wealthy Russian an arm and a leg.” The film closes with Johnny proclaiming that with his new freedom, he will do what he couldn't do before: “become a real RocknRolla”. The end credits suggest there will be a sequel titled “The Real RocknRolla”.