Mrs. Montague and Mr. Capulet, two elderly neighbors portrayed by Julie Walters and Richard Wilson respectively, harbor a deep disdain for one another. Once they step away from their gardens, something magical occurs— their lawn ornaments and gnomes come to life. In the Montague garden, a troupe of blue-hat gnomes, led by the formidable Lady Bluebury, face off against the red-hat gnomes commanded by Lord Redbrick, played by Michael Caine. Mirroring the animosity of their human counterparts, the gnomes are locked in a bitter rivalry.
The tension escalates when the gnomes organize an underground lawnmower race. Lady Bluebury's son Gnomeo, in his blue gear, competes alongside his best friend Benny, while Tybalt, embodying the fierce leader of the reds, resorts to underhanded tactics to secure victory, resulting in Gnomeo's lawnmower getting wrecked. Disheartened, Gnomeo and Benny watch as Mrs. Montague orders a shiny new "Kitty Clipper" lawnmower to replace the damaged one.
That evening, a daring escapade leads Gnomeo and Benny into the forbidden red garden, cloaked in disguises. An eventful encounter unfolds when Gnomeo stumbles upon Juliet, the daughter of Lord Redbrick, who is secretly on a quest to retrieve a rare orchid. They engage in a playful, yet romantic skirmish over the flower, but eventually realize their true colors before making a hurried exit back to their respective gardens. Back home, Juliet confides in her playful friend Nanette about her blossoming feelings, to which Nanette ominously predicts a tragic love story.
As Gnomeo and Juliet embark on secret rendezvous, they cross paths with a whimsical pink flamingo named Featherstone, who becomes their unexpected supporter. However, trouble brews when Lord Redbrick attempts to match Juliet with a red gnome named Paris, leaving her uninterested. To evade a dull fate, she distracts Paris with Nanette's affections.
Amidst all this, Lady Bluebury is heartbroken after a raid by the reds, resulting in the destruction of a cherished plant nurtured by Gnomeo's late father. Pressured by his blue comrades for revenge, Gnomeo grapples with his moral compass. Just as he is about to enact vengeance by damaging the reds' prized tulips, Juliet intervenes, causing him to reconsider.
Their reunion takes a tumultuous turn when Featherstone intervenes, sharing his own loss, a cautionary tale of love destroyed by separation. Meanwhile, a confrontation ensues between Gnomeo and Tybalt, leading to a chaotic lawnmower showdown, which climaxes in Tybalt's unfortunate accident, sparking outrage among the reds who mistakenly believe Gnomeo caused his injury. In a surprising move, Juliet publicly defends Gnomeo, declaring her love for him.
As Gnomeo's fate hangs in the balance, the tension escalates when Lord Redbrick, fearing another loss, resorts to desperate measures by gluing Juliet to her fountain, preventing her from leaving him. After a series of events, Gnomeo learns that he is still alive and seeks out his beloved.
A comedic turn of events results when Benny hacks into Mrs. Montague’s computer, ordering a colossal lawnmower intended for vengeance, but it wreaks havoc instead, entangling both gardens in a chaotic battle. Gnomeo manages to reach Juliet with Featherstone's help, only for disaster to strike as the Terrafirminator malfunctions, wreaking further destruction. The two share a heart-stopping moment just as the lawnmower crashes, leading everyone to believe they have perished.
In a surprising twist, Gnomeo and Juliet emerge from the wreckage, prompting both families to reconcile. As the red and blue gnomes celebrate the newfound peace, Tybalt is discovered to be alive, mended by glue. Featherstone gets reunited with his long-lost wife thanks to Benny’s efforts. Ultimately, Gnomeo and Juliet solidify their love with a wedding ceremony on a purple lawnmower, symbolizing the joyous union of their two worlds.
