The first time Saoirse Ronan and Margot Robbie saw each other in character was during the scene where they meet for the first time. They rehearsed separately, and Robbie's scenes were completed the day Ronan began hers.
Director Josie Rourke had to convince the studio not to delete the scene where Queen Mary Stuart (Saoirse Ronan) has her period. She stated that "those were instructive discussions about how honest we were being about women's bodies and what they do, women's pleasure and what that is, and a Queen's body as a political canvas." She added that "it happens to half of us," so "we need to show this stuff. It does need normalizing."
Queen Elizabeth I never ruled Scotland, which led to protests about the regnal number II used by the late Queen Elizabeth II. In the 1950s, after Elizabeth ascended to the throne, a post box in Scotland marked "EIIR" was blown up, and lawyer Ian Hamilton fought a court case against the use of "Elizabeth II" in Scotland. The lyrics of the folk song "Coronation Coronach" include the lines "Hou can ye hae the Second Liz/Whan the First yin's nivver been?"
Margot Robbie was initially reluctant to accept the role of Queen Elizabeth I. She accepted after receiving a letter from director Josie Rourke about why she wanted Robbie in the role.
It's not mentioned in this movie, but Queen Elizabeth I also claimed the throne of France.