The film received critical acclaim and was a box office success. Both Gleeson and Cheadle received acclaim for their performances, with Gleeson receiving a Golden Globe Award nomination. McDonagh was in turn nominated for a BAFTA Award for his writing achievement.
Gerry Boyle (Brendan Gleeson) is a Sergeant in the Garda Síochána, stationed in the Connemara Gaeltacht of western Ireland. He is crass, confrontational, and regularly indulges in alcohol, narcotics, and prostitutes while on duty. Despite this, Sgt. Boyle lives by a very strict ethical code and shows love and concern for his ailing mother, Eileen (Fionnula Flanagan). Boyle joins his new subordinate, Garda Aidan McBride (Rory Keenan), to investigate a murder in their jurisdiction, with evidence apparently pointing to an occult serial killer. Shortly after, Boyle attends a briefing by FBI Special Agent Wendell Everett (Don Cheadle). Agent Everett has been sent to liaise with the Garda in hunting down four Irish drug traffickers, led by Francis Sheehy-Skeffington (Liam Cunningham), who are believed to have arranged a seaborne shipment of cocaine worth an estimated US$500 million (US$0.5 billion). To Everett's shock, Boyle recognises one of the men in Everett's slide show as the victim of the murder he and McBride had been investigating.
As Boyle drives Everett to the crime scene, Garda McBride pulls over a speeding car driven by Sheehy and his lieutenants Clive Cornell (Mark Strong) and Liam O'Leary (David Wilmot). After Sheehy sadistically boasts that he knows all about him, Garda McBride is shot dead. Garda McBride's wife, Gabriela (Katarina Čas), reports her husband's disappearance to Boyle. A Croat national, she explains that her marriage to Garda McBride was arranged so that she could gain an Irish visa. As her husband was secretly a homosexual, it also allowed him "to look respectable." Suspecting the worst, Boyle promises to look into it.
The strait-laced Everett decides that he and Boyle should team up to track down Sheehy and his men. Unimpressed, Boyle announces that he has better things to do. Later, while Everett makes the rounds, he encounters Irish-speaking residents who refuse to answer him in English and the traditional Irish refusal to assist law enforcement. Boyle has a sexual encounter with two prostitutes, Aoife (Dominique McElligott) and Sinéad (Sarah Greene), at a hotel. On his drive back from the hotel, Boyle spots McBride's Garda car at a local "suicide hotspot" along the coast, but does not believe that McBride killed himself. Meeting Everett at a local bar, Boyle listens as Everett laments that law enforcement in Ireland is just like trying to investigate gang violence in Compton. Boyle notices a CCTV camera and remembers that the original suspect in the first murder claimed to be frequenting the very same establishment at the time of the killing.
Looking over the footage from the time of the murder, they see that the suspect's alibi is valid – and a stunned Everett also spots Sheehy and Cornell at the bar at the same time. Meanwhile, Cornell delivers a bribe to Boyle's Garda superiors, who promise to divert manpower away from the shipment when it arrives in Spiddal. They warn, however, that Boyle "is too unpredictable" and will cause trouble for them. After brutally beating one of Boyle's favorite call girls, Sheehy arranges a meeting with him. Sheehy threatens to use Boyle's encounter with the two prostitutes to get him fired and then offers him a bribe. After expressing his hatred for "cunts who beat up on women", Boyle shocks Sheehy by contemptuously refusing the money.
Tipped off by a young boy named Eugene (Michael Og Lane), Boyle discovers a weapons cache hidden in a local bog by the Provisional IRA and arranges its return to them. The IRA man expresses shock that the cache is now missing an AK-47, a Glock pistol, and a derringer pistol. After acting insulted, Boyle is promised that the IRA will do him any favor he asks in return. After having her last wish to hear a live pub band fulfilled, Boyle's mother dies.
Meeting at the bar again, Everett tells Boyle that Garda sources indicate Sheehy's shipment will be coming into County Cork and that he is leaving to investigate. Returning home, Boyle is confronted in his living room by O'Leary, who has been ordered by Sheehy to kill him. Holding the Sergeant at gunpoint and visibly enjoying himself, O'Leary boasts that Garda McBride was buried at sea and that "little fishies will have eaten him by now." The drugs will be landed in Spiddal that very night and the trio's Garda protectors have ordered all personnel to be far away.
Much to O'Leary's amusement, Boyle begins scratching his groin. Believing that the Sergeant caught crabs from a prostitute, O'Leary quips that he has only himself to blame. To his shock, however, Boyle pulls out the derringer from the cache and fatally shoots O'Leary. As the gangster's life drains away, Boyle mocks his bottomless self-pity and calls Everett to tell him that the Cork lead is a decoy arranged by corrupt officers. As Everett drives to Spiddal, Boyle tells Gabriella, whom he now has feelings for, of her husband's murder. Although she clearly loves him, too, and begs him not to leave, Boyle insists that he needs to do so. As Gabriella dissolves into tears, Boyle drives towards Spiddal.
As Sheehy's vessel is berthed and Sheehy's men unload the cocaine, Everett arrives and is horrified by Boyle's description of corruption in the Garda. Boyle laments that Sheehy’s corrupt Garda protectors will never forget or forgive what he is about to do. Therefore, he may have to disappear. Boyle arms himself with a pistol from the arms cache, and offers the AK-47 to Everett, telling him there is now only one way to bring the trio to justice. He urges Everett to give him covering fire as he moves to arrest Sheehy and Cornell. At first Everett balks at Boyle's plan, saying that for him to fire an illegal firearm in the middle of Ireland "will cause an international incident." He relents, and opens fire as Boyle – taking a flesh wound to the arm – shoots Cornell and leaps onto the boat in pursuit of Sheehy.
As Everett’s gunfire sets the boat alight, Boyle shoots Sheehy and leaves him to burn alive in the main cabin as the boat explodes. The next day, a despondent Everett looks out over Galway Bay, believing Boyle to be dead. Eugene, standing nearby, mentions that Boyle was a good swimmer, having claimed to have been placed fourth at the 1988 Summer Olympics in Seoul, a claim that Everett had incredulously dismissed. A young photographer (Laurence Kinlan) comments that it would be easy enough to look up. The film then flashes back to Everett's comment that he couldn't decide whether Boyle was really dumb or really, really smart. Back in the present, Everett smiles to himself, having finally found the answer.
The credits roll to John Denver's "Leaving on a Jet Plane", hinting that Boyle survived and chose to leave Ireland.Brendan Gleeson as Sergeant Gerry Boyle
Don Cheadle as FBI Agent Wendell Everett
Mark Strong as Clive Cornell
Liam Cunningham as Francis Sheehy-Skeffington
Fionnula Flanagan as Eileen Boyle
Michael Og Lane as Eugene Moloney
David Wilmot as Liam O'Leary
Sarah Greene as Sinéad Mulligan
Darren Healy as Jimmy Moody
Rory Keenan as Garda Aidan McBride
Dominique McElligott as Aoife O'Carroll
Katarina Čas as Gabriela McBride
Dermot Healy as old farmer
Pat Shortt as Colm Hennessy
Laurence Kinlan as young photographer
Film producers include Chris Clark, Flora Fernandez-Marengo, Ed Guiney and Andrew Lowe, with executive producers Paul Brett, Don Cheadle, Martin McDonagh (brother of John Michael), David Nash, Ralph Kamp, Lenore Zerman and associate producer Elizabeth Eves. Director John Michael McDonagh is known for his screenplay for the 2003 film Ned Kelly and as writer/director of the 2000 film The Second Death. Cinematographer Larry Smith is known for his work on Eyes Wide Shut and production designer John-Paul Kelly for his work on Venus.
Principal filming began on 29 October 2009, in Leitir Móir (Lettermore) County Galway. Filming took place over a six-week period in Connemara, Leitir Móir, Leitir Mealláin (Lettermullen), An Spidéal, and Bearna with some scenes for filming in Wicklow and Dublin. Involved companies are Reprisal Films and Element Pictures in association with Prescience, Aegis Film Fund, UK Film Council and Crescendo Productions, with the participation of An Bord Scannán na hÉireann (Irish Film Board).
International sales were handled by Metropolis Films and the film was released by Element Pictures Distribution in Ireland, Optimum Releasing in the United Kingdom, Sony Pictures Classics in the United States and Alliance Films in Canada.
Reviews for The Guard were overwhelmingly positive. The review aggregator website Rotten Tomatoes reported a 94% approval rating with an average rating of 7.6/10 based on 125 reviews. The website's consensus reads, "A violent, crackerjack comedy with a strong Irish flavor and an eminently likable Brendan Gleeson in the main role." On the review aggregator Metacritic, the film has a score of 78 out of 100, based on 29 critics, indicating "generally favorable reviews".
In The Hollywood Reporter, Todd McCarthy wrote: "Scabrous, profane, violent, verbally adroit and very often hilarious, this twisted and exceptionally accomplished variation on the buddy-cop format is capped by a protean performance by Brendan Gleeson a defiantly iconoclastic West of Ireland policeman." Vanity Fair's John Lopez wrote: "So far, The Guard has been the most thoroughly enjoyable film experience at Sundance, a nice change of pace from the anomie, alienated angst and melancholy of other films. In Screen International, David D'Arcy wrote: "As a director, McDonagh avoids the grand gesture and focuses on his web of odd characters that call to mind the comedies of Preston Sturges." Justin Chang of Variety wrote: "The film making crackles with energy, from Chris Gill's crisp editing and Calexico's ever-inventive score to d.p. Larry Smith's dynamic camerawork, alternating between bright, almost candy-coloured interiors and shots of Galway's grey, rugged landscape."
In The Times, Wendy Ide wrote: "Without doubt the strongest debut film of the year so far, this sly, witty and provocative Irish black comedy is an exceptionally funny crowd-pleaser and a playful cine-literate exercise, laced with arcane movie references... Gleeson must be thanking whatever guardian angel oversees his career for the brothers McDonagh giving him two of his meatiest roles yet." Georgie Hobbs of Little White Lies wrote: "Unexpectedly hilarious, The Guard is the triumphant directorial debut of Ned Kelly screenwriter (and brother of In Bruges director Martin), John Michael McDonagh... This confident film knows full well how funny it is, daring to provoke with unfettered 'unPCness' a-plenty."