Set against the vibrant backdrop of Dublin in 1985, 15-year-old Conor Lalor (Ferdia Walsh-Peelo) finds solace in his bedroom, strumming his guitar. However, the harmony of his life is disrupted when he overhears his parents, Robert (Aidan Gillen) and Penny (Maria Doyle Kennedy), arguing, which inevitably inspires his songwriting.
In a tense family meeting in the kitchen, Conor learns that due to financial struggles, his parents have decided to enroll him in a free state school instead of continuing at his current institution. His older brother, Brendan (Jack Reynor), a dropout with a penchant for sarcasm, doesn’t hold back on his comments about the situation, further complicating Conor's quest for identity.
Starting a new chapter at Synge Street CBS, Conor's initial encounter with the strict principal, Brother Baxter (portrayed by Don Wycherley), underscores his struggle: he only owns brown shoes, while the school insists on a strict black shoe policy. Shortly after, Conor has a humiliating run-in with the school bully, Barry (Ian Kelly), who forces him to dance under duress. Conor's resilience starts to blossom when he befriends Darren (Ben Carolan), who helps him navigate the challenges ahead.
One fateful day, Conor's attention is drawn to a striking girl across the street, Raphina (Lucy Boynton), whom Darren claims is uninterested in their schoolmates. Undeterred, Conor takes a chance, introducing himself and inviting her to star in a video for his newly formed band. Raphina, cheeky and confident, agrees – under a condition that he serenades her. With limited options, he half-heartedly sings two lines from a-ha's “Take On Me”, which surprisingly leads Raphina to agree to the gig, propelling Conor into the thrilling world of music.
In his quest to form a band named "Sing Street," Conor collaborates with talented schoolmates, such as Eamon (Mark McKenna), who becomes the bass guitarist, and Ngig (Percy Chamburuka), the keyboardist. Their line-up expands with Larry (Conor Hamilton) and Garry (Karl Rice), while Darren assumes the role of the band’s enthusiastic manager. Eager to impress, they cover Duran Duran's "Rio," though Brendan’s unfiltered critique pushes Conor to channel his creativity towards writing original music.
With the hopeful encouragement of Eamon, Conor pens their first original song, "The Riddle of the Model," a heartfelt tribute to Raphina. He records a demo, sharing it with her, marking the start of an exhilarating journey. The band shoots their first video, where Raphina brings glam to the boys, but their budding relationship takes a serious turn when Conor learns about her complicated past and current relationship with an adult man.
Despite his awkward situation involving makeup and the wrath of Brother Baxter, Conor dives further into his creative pursuits, ultimately leading to a pivotal moment during the shoot for "A Beautiful Sea." Their daring antics culminate in a kiss, deepening their connection against all odds.
As their friendship grows, Raphina introduces Conor to the idea of living with a "happy-sad" mindset, encouraging him to embrace the world's challenges while expressing himself through art. Conor’s newfound confidence allows him to face Barry without fear, leading to decisive moments at school when they seize the opportunity to perform at a dance.
A journey across Dalkey Island shared over tea solidifies their bond, offering a fleeting escape from their harsh realities. However, personal turmoil strikes when Conor’s parents announce their separation, further complicating his emotional landscape. Brendan, struggling with his own feelings of inadequacy, turns to anger while Conor is forced to confront the painful truths surrounding love and ambition.
On the night of the dance, the band electrifies the atmosphere, uniting the students with their infectious energy. When Conor lovingly introduces a slow song, the compelling ambiance transforms into a mix of joy and heartbreak as he shares a moment with Raphina. In a bittersweet twist, she arrives just in time to witness his heartfelt performance.
In the midst of all this chaos, a pivotal decision is made that sees Conor and Raphina embarking on a spontaneous adventure to London. As Brendan drives them to the coast, he offers a hopeful goodbye, leaving Conor to navigate his future with Raphina. Amidst pouring rain, they board a ferry to England with dreams in their eyes, ready to chase the horizon together.
