The film opens with Elle Evans (Joey King) reflecting on her relationship with Noah Flynn (Jacob Elordi) as he prepares to leave for Harvard. As her senior year commences, rumors swirl among her classmates suggesting that her romance with Noah is fated to fail. A spike of jealousy arises within Elle as Noah strikes up a friendship with the charming British girl, Chloe Winthrop (Maisie Richardson-Sellers), through social media. On the flip side, Noah grapples with feelings of neglect, urging Elle to be closer to him, while he prompts her to consider applying to Harvard—a move that complicates her plans of attending the University of California, Berkeley with her best friend, Lee Flynn (Joel Courtney), where their mothers initially bonded.
In a bid to raise funds, Elle and Lee decide to resurrect their popular kissing booth for the upcoming Charity Fair. Lee proposes that the cute newcomer, Marco Peña (Taylor Zakhar Perez), take part as one of the kissers, igniting a mix of enthusiasm and apprehension in Elle. Amidst a series of comedic mishaps, including an accidental on-air blunder involving Marco's workout video, Elle finds herself increasingly at odds with her feelings. A rivalry emerges as they compete for the highest score on their favorite dancing game at the arcade, with Marco claiming the title of “MVP.”
Things escalate when Elle pays a visit to Noah in Boston, feeling insecure as she meets his new friends, including Chloe. During a college interview, an insightful remark from one of the interviewers resonates with Elle: she should embrace her true self instead of conforming to someone else’s expectations. Suspicion brews when Elle discovers an earring under Noah's bed, leading to an emotional confrontation where Noah reassures her of his fidelity. Meanwhile, financial pressures loom over Elle's dreams of college, prompting her and Lee to join a dance competition that offers a $50K prize.
When Marco steps up as her dance partner after a fabricated accident sidelines Lee, an undeniable chemistry sparks between them. However, Noah's concert date with Chloe leaves Elle feeling betrayed, exacerbating tensions among friends. Elle's unyielding involvement in Lee's relationship with Rachel (Meganne Young) leads to friction as Lee struggles to find private moments with Rachel.
The much-anticipated Halloween Dance arrives, marked by costume mix-ups and romantic near-misses. On competition day, when Lee discovers Elle's secret college applications, their friendship strains further. Right at the climax of their dance performance, Elle and Marco share a kiss just as Noah watches in dismay from the audience, prompting her to chase after him.
During Thanksgiving at the Flynn household, the dynamics shift dramatically. When Noah appears with Chloe, tensions surface, culminating in confrontations about Elle's decision to apply to Harvard. Amid revelations and emotional upheavals, Rachel decides to part ways with Lee when she realizes he upheld none of her needs for space.
As the carnival day approaches, love seems to find its way back. Lee and Rachel reconcile through a tender kiss at the booth, lending hope for their friendship with Elle, who flirts with the idea of pursuing Marco. When she finally decides to seek out Noah, Chloe reveals his whereabouts at the park where they first shared a kiss. This reunion unravels as Noah admits to his insecurities about college while expressing his desire to replicate the close bond Elle has with Lee.
Fast forward six to seven months, and graduation dawns for Elle, Lee, and Rachel. News arrives for Elle about her college applications: she is wait-listed at both Berkeley and Harvard, sending her into a whirl of contemplation. As Marco looks on from a distance, questioning his own feelings, Elle opens two envelope letters in her room, a pivotal moment revealing her acceptance into both prestigious universities, forcing her to make a life-altering decision: Harvard with Noah or Berkeley with Lee.
