On the stunning Greek island of Kalokairi, 20-year-old bride-to-be Sophie Sheridan (Amanda Seyfried) decides to take a bold step towards finding her father by sending out three wedding invitations. Each invitation is addressed to a potential father: the New York-based Irish architect Sam Carmichael (Pierce Brosnan), the adventurous Swedish writer Bill Anderson (Stellan Skarsgård), and the British banker Harry Bright (Colin Firth). As the wedding date approaches, Sophie's excitement builds alongside the drama of her impending nuptials.
Arriving before the wedding are Sophie's best friends, Ali and Lisa (Ashley Lilley and Rachel McDowall), who soon find themselves entangled in Sophie's secret quest. Sophie reveals that she discovered her mother Donna Sheridan's (Meryl Streep) diary, which led her to uncover the identities of her three possible fathers. With a heart full of hope, she believes that by spending time with these men, she will uncover the truth about her parentage and avoid making the same mistakes her mother made. During this time, Donna is thrilled to reconnect with her old bandmates, the witty writer Rosie (Julie Walters) and the affluent divorcee Tanya (Christine Baranski), while reflecting on her complex feelings about Sophie's forthcoming wedding.
As the three men arrive, Sophie sneaks them into their accommodations, pleading with them to keep their identities secret from Donna to create an unforgettable surprise. Tensions rise when Donna unexpectedly encounters them and is left stunned by the presence of her past lovers—each reminding her of moments long buried. In a moment of vulnerability, Donna confides in Rosie and Tanya about her uncertainty regarding which man could truly be Sophie's father, leading to a heartfelt exploration of love and regret.
Sophie, meanwhile, spends time with each of the potential fathers, sailing around the breathtaking Kalokairi on Bill's yacht, where anecdotes about Donna's youthful adventures flow freely. Caught in a web of emotions, Sophie grapples with her conscience regarding her secret as her fiancé Sky (Dominic Cooper) prepares for his bachelor party. During a wild hen party, Donna and her friends evoke nostalgia by performing with their old band, Donna and The Dynamos.
Complications deepen as the night unfolds, revealing long-buried connections and the realization of shared feelings among the men and Donna. Sophie, distracted and overwhelmed, faints after being bombarded by their expectations. The next day, feeling a need to mend the growing rift with her mother, she finds herself confessing her fears to Donna, who helps her prepare for the wedding while reminiscing about their shared past.
As the ceremony approaches, the entwined destinies of Sophie, Donna, and the three men collide. Secrets are laid bare, and desire reignites, bringing to light the choices made long ago. A dance-filled reception takes a whimsical turn, and amidst heartfelt proclamations of love, the ground beneath them erupts, revealing the mythic fountain of Aphrodite. In a stunning finale, Sophie and Sky decide to postpone their wedding to explore the world together, while Sam proposes to Donna, culminating in a joyous gathering where couples unite in celebration, paying homage to the enduring power of love and connection. As the couples raise their voices in a triumphant finale, Sophie and Sky sail away, filled with dreams of what is yet to come.
