Director Rupert Everett had written promises from his friends Colin Firth and Emily Watson that they would participate in this movie if he ever got it made, and he would often half-jokingly remind them when he saw them. Even when Firth became famous and his busy schedule made it unsure if he would be able to keep his promise, Everett got funders aboard and people to participate by stating that Firth had already signed on. Near the end of production, when the movie ran out of budget, Firth even agreed to waive his salary, so he basically did the movie for free.
This is Rupert Everett's writing and directing debut. Everett tried to get his passion project made for ten years, rejecting other movie roles so he would be available if it was green-lit.
When Oscar Wilde gets his hair cut shortly after arriving in Reading Gaol, Rupert Everett gets his actual hair cut until he's bald. This was done on one of the first days of shooting and Everett wore a wig for the rest of the movie.
Colin Firth and Rupert Everett had started their careers around the same time and had initially been quite good friends. However in the 1990s they stopped talking to each other after Everett became a star and started dabbling in drugs, drinking too much and mixing with new celebrity friends (or as Everett readily admitted; "It was all my own stupid fault. I was out of control and only had myself to blame"). Firth would eventually find fame several years later and watched as Everett's career took a distinct downturn. When this film became a passion project for Everett around 2015 and he was working out how to make it. He tentatively approached Firth but expected to be given short shrift after having not spoken to him for around 20 years. To his amazement not only did Firth readily accept but said he would sink some of his own money into the production to help get it off the ground. Everett said he was so happy that Firth had been so understanding and forgiving to him and the two are now happily back on good terms.
Oscar's statement that he is "in mortal combat" with the wallpaper and that one of them has to go, is based on a well-known quote of the real Oscar Wilde that he made in his final weeks when he had settled in a room in the Hôtel d'Alsace in Paris. The quote is often misreported as his dying words.