In August 2018, Hildur Guðnadóttir was hired to compose the film's score.[124] Hildur began writing music after reading the script and meeting with Phillips, who "had a lot of strong ideas" about how he thought the score should sound. She worked on the Joker score alongside the score for the drama miniseries Chernobyl; Hildur told The Hindu's Divya-Kala Bhavani switching between the two was challenging because the scores were so different.[125]
Additionally, the film features the songs "That's Life", "Send In the Clowns", "White Room" and "Rock and Roll Part 2".[41][126] The use of "Rock and Roll Part 2" generated controversy when it was reported that its singer, convicted child sex offender Gary Glitter, would receive royalties, but it was later confirmed he would not.[126] The score was released on October 2, 2019, by WaterTower Music.[127] Hildur's music won numerous awards including an Academy Award, a Satellite Award, a Saturn Award, the Hollywood Music in Media Awards (HMMA) and the Golden Globe Award for Best Original Score, with the latter making her the first woman to win as a solo composer in that category.[128][129]
