Two longtime friends, Justin Miller (Wayans), a struggling video game designer, and Ryan O'Malley (Johnson), an unemployed, washed-up former college quarterback, recall a pact they once made: if they hadn't "made it" in Los Angeles by the time they were thirty, they would head back to their Columbus hometown. As they leave a bar, their car is hit by an Mercedes Benz G500 driven by an Albanian gang, who intimidate them into not retaliating.
Justin attempts to pitch a video game about policemen but the idea is rudely dismissed by his boss Todd. Later, Ryan convinces him to use the police uniforms from his presentation as costumes for their college reunion party. Upon attending, they meet many successful former classmates and both are confronted with a sense of failure and they mutually accept to honor their pact. As they walk home, they are treated like real cops and decide to enjoy the gag. They kick the Albanian gang out of Georgie's, a local diner. It allows Justin to finally get the attention of Josie, a waitress to whom he is attracted and who works at the said diner.
Ryan decides to take the hoax further than one night. He learns official procedures on YouTube and buys a used Ford Crown Victoria police cruiser, modifying it with decals to resemble a real LAPD car. Although reluctant, Justin agrees to continue the charade, and through it begins a relationship with Josie. Ryan gets revenge on the Albanians who hit his car, unaware they are actually mobsters blackmailing the owner of Georgie’s. During their many shenanigans, Ryan and Justin end up on a real distress call with Patrol Officer Segars. The experience shakes Justin, who realizes they face serious jail time if exposed. He tries to “retire,” but gets a phone call from Josie about a man frequently harassing her at work. It turns out to be Mossi Kasic, the leader of the same Albanian gang. Once more, the pair are intimidated into doing nothing.
Via Segars, Ryan obtains surveillance equipment to gather evidence and put Mossi away, along with an unidentified partner who has been investigating the pair. Ryan convinces Justin to do an undercover operation to obtain information on an incriminating shipment of crates. During the mission, they discover the crates full of SWAT equipment and weapons, along with secret tunnels that run between Mossi's club and Georgie’s restaurant. This necessitates the acquisition of the restaurant, explaining the blackmail. After a few close encounters with the mobsters, they barely escape. Fed up, Justin insists on mailing the evidence anonymously, but Ryan, finding purpose in his life again, is set on delivering it personally. They fight, and part ways.
Ryan brings his evidence to Segars, who recommends it go to the highest authority, which is Detective Brolin. Unfortunately, Brolin is actually Mossi's business partner. After instantly recognizing each other, Ryan makes it out of the station, but his sudden threat has blown their cover. Meanwhile, Justin decides to "man up" and, in uniform, assertively pitches his game again. One of Brolin's officers shows up to try and kill him, inadvertently helping to sell the pitch. Ryan is abducted, and Mossi sends a threatening message to Justin. Overwhelmed, Justin pleas to Segars for help after admitting everything. He also confesses to Josie that he is not a real cop, which he had made previous attempts to do, and she disgustedly leaves him.
Justin goes into the tunnels alone while Ryan pits Mossi and Brolin against each other, prompting Mossi to shoot and kill the detective. Justin attempts to save his friend, but is overpowered. Segars arrives, causing Mossi and his crew to retreat. Segars admonishes the duo for their deception and orders them to leave before going after the mobsters, without waiting for backup. Ryan and Justin agree they can’t abandon him, and suit up with the SWAT equipment. They save Segars, but he becomes incapacitated. The pair then face Mossi alone, during which the two reconcile. They fail to take him out, but luckily, Segars is able to show up and shoots Mossi on the side of the neck, saving Justin and Ryan.
Thanks to the respective confidence and motivation gained during their impersonations, Justin has become a successful game developer, while Ryan graduates from the police academy as a true, fully-fledged member of the LAPD. Justin apologizes to Josie, and after she forgives him, they rekindle their relationship. Ryan, however, still has not given up on their fun as cops together, and convinces Justin to don the fake uniform once again and join him on patrol.
Principal photography began in May 2013 in Atlanta, Georgia, some of the filming also took place in Charleston, SC, and wrapped up in July.
The film was released on August 13, 2014 with an R rating in America and a 15certificate in the UK.
Let's Be Cops grossed $82.4 million in North America and $55.8 million in other territories for a total gross of $138.2 million, against a budget of $17 million.
The film grossed $8.4 million on Wednesday and Thursday, and $17.8 million in its opening weekend, finishing in third at the box office behind Teenage Mutant Ninja Turtles ($28.5 million) and Guardians of the Galaxy ($25.1 million), but the first among the weekend's new releases.
On Rotten Tomatoes, the film has an approval rating of 19% based on 75 reviews and an average rating of 3.9/10. The site's critical consensus reads, "Damon Wayans, Jr. and Jake Johnson have comedic chemistry; unfortunately, Let's Be Cops fails to do anything with it." On Metacritic, the film has a score of 30 out of 100 based on 23 reviews, indicating "generally unfavorable reviews". Audiences polled by CinemaScore gave the film an average grade of "B" on an A+ to F scale.
Time magazine placed Let's Be Cops fifth in their ranking of the 10 worst movies of 2014, stating: "The initial setup of Let's Be Cops could have been a funny premise for a B-plot on a show ... but instead, the idea is stretched into a never-ending feature that fails to find any chemistry between Johnson and Wayans".