Joanna Hogg wrote the script based on her real-life experiences while attending film school in London in the early '80s. Tilda Swinton and Hogg have been friends since they were ten years old, and Swinton witnessed Hogg's relationship at the time. All actors read the script except for Honor Swinton Byrne. Director Joanna Hogg gave her instead her diaries from the early '80s, notes, photographs, and old scripts and films she wrote and made at that time. She was told to improvise every scene, while the rest of the cast had scripts but were still told to react to her as well as they could. Hogg also gave Tom Burke old letters, recordings, and drawings from the man his character is based on.
Honor Swinton Byrne is the real-life daughter of Tilda Swinton. The Souvenir (2019) and The Souvenir: Part II (2021) are her first film roles after playing the child version of Tilda Swinton's character in I Am Love (2009) 10 years earlier.
The films title 'The Souvenir' is named after an 18th century rococo painting of the same name by Jean-Honoré Fragonard, which features a woman scratching the initials of her lover onto a tree.
Julie's London flat is a perfect replica of the one that director Joanna Hogg lived in at that age. The set was built inside of an airplane hanger, and the city views seen through the windows are 35mm projections of photographs that Hogg took in her twenties.
Joanna Hogg already cast Tom Burke and Tilda Swinton, but couldn't find the right girl to portray Julie until just weeks before filming was supposed to start. When she met with Tilda Swinton to discuss her part, her daughter Honor Swinton Byrne happened to be there by coincidence and Hogg suddenly started to see Julie in her. Swinton and Hogg had been friends since they were ten, so Hogg already knew Honor, but Hogg never thought about giving the role to Honor because she had never acted before.