To prep for the film, Will Ferrell attended the 2018 Eurovision Song Contest Lisbon 2018 (2018) in Lisbon, Portugal as part of the Swedish delegation and was given access to follow the show from start to finish, including rehearsals.
Will Ferrell's interest in the Eurovision Song Contest began when his Swedish wife Viveca Paulin took him to her cousins house in May 1999 and the family turned the competition on. Since then, he kept following it. In 2014, Ferrell travelled to Copenhagen, Denmark to watch the finale of Eurovision Song Contest Copenhagen 2014 (2014), in which Conchita Wurst was crowned the winner.
Despite playing a singer, Rachel McAdams does not perform her character's singing. Her character's vocals are actually performed by Swedish singer Molly Sandén, who was part of Junior Eurovision Song Contest (2006), Melodifestivalen 2009 (2009) and Melodifestivalen 2016 (2016). Sandén is credited as My Marianne which is her middle name. McAdams did record the songs and her vocal was added for additional mixing, and her vocal can be heard during the first EuroVision rehearsal and when Sigrit is writing "Husavik" in her hotel room. Dan Stevens' singing voice is also dubbed by another Swedish singer, Erik Mjönes, while Melissanthi Mahut is dubbed by Petra Nielsen.
The film features appearances from past Eurovision contestants: John Lundvik (Sweden 2019), Anna Odobescu (Moldova 2019), Bilal Hassani (France 2019), Loreen (winner for Sweden in 2012), Jessy Matador (France 2010), Alexander Rybak (winner for Norway in 2009 & representative in 2018), Jamala (winner for Ukraine in 2016), Elina Nechayeva (Estonia 2018), Conchita Wurst (winner for Austria in 2014), Netta Barzilai (winner for Israel in 2018) and Salvador Sobral (winner for Portugal in 2017).
Will Ferrell's singing voice was not dubbed, he is actually singing.