Following his graduation from university, aspiring filmmaker Colin Clark (Eddie Redmayne) makes his way to London with dreams of working on the next production of renowned actor Laurence Olivier (Kenneth Branagh). Despite being told by Hugh Perceval ([Michael Kitchen]) that no positions are available, Colin decides to wait for Olivier, with whom he once shared a brief encounter at a party. When Laurence and his wife, Vivien Leigh (Julia Ormond), finally arrive, Vivien lends her support, encouraging Olivier to hire Colin for the upcoming film "The Prince and the Showgirl," which stars the iconic Marilyn Monroe (Michelle Williams).
Colin's first mission is to find suitable accommodations for Marilyn and her husband, Arthur Miller ([Dougray Scott]), as they settle into England. When the media catches wind of their arrival, Colin cleverly secures a second location, impressing both Olivier and Marilyn's publicist, Arthur Jacobs ([Toby Jones]).
Upon landing at Heathrow, Marilyn arrives with her husband, business partner Milton H. Greene ([Dominic Cooper]), and acting coach Paula Strasberg ([Zoë Wanamaker]). Initially shy around the throngs of paparazzi, she gradually warms up during a press conference. However, her tardiness to the read-through soon frustrates Olivier, especially when she requires Paula's assistance with her lines. The crew, along with veteran actress Sybil Thorndike ([Judi Dench]), are in awe of Marilyn’s presence, while Colin finds himself drawn to wardrobe assistant Lucy ([Emma Watson]). Their budding romance leads to a date.
As production continues, Marilyn's pattern of arriving late and forgetting her lines further irritates Olivier. Yet, Sybil stands up for her, recognizing the struggles Marilyn faces. When tensions rise, and after receiving an insulting remark from Olivier, Marilyn walks off set. Colin, showing compassion, asks Olivier for more understanding and later visits Parkside House to check on her. There, he finds Marilyn in tears, clutching Arthur's notebook, which appears to mock her. Arthur soon returns to the US, leaving Marilyn disheartened.
Vivien, watching the turmoil from the sidelines, is visibly moved by Marilyn's screen presence, lamenting that Olivier fails to appreciate the light she brings. With Arthur gone, Marilyn refrains from attending the set and invites Colin to her residence, deepening their connection. As Marilyn prepares for a scene, she enchants the crew with a dance, leading to Milton cautioning Colin about the nature of their relationship. Lucy, sensing the growing affection between Marilyn and Colin, decides to end their relationship.
Colin and Marilyn share a memorable day at Windsor Castle and Eton College, culminating in a forbidden skinny-dip in the River Thames. Their chemistry intensifies when Marilyn kisses Colin, only to be interrupted by her bodyguard, Roger Smith ([Philip Jackson]). Later, Marilyn contacts Colin in distress, claiming she is having a miscarriage. A doctor arrives to aid her, and she confides in Colin, expressing a desire to escape her troubles.
Despite her challenges, Marilyn returns to complete the film, where Olivier praises her work, albeit revealing that she has extinguished his desire to direct again. When Lucy inquires whether Marilyn has broken Colin's heart, he admits, “she did, a little.” In a heartfelt farewell, Marilyn visits Colin at his B&B, thanking him for his support and sealing their brief but impactful connection with a kiss before she leaves for the airport, driven away by Roger.
