Masterson joined the D'Oyly Carte Opera Company as a principal soprano in 1964. After a performance as Mabel in The Pirates of Penzance, The Guardian commented, "It is Valerie Masterson's Mabel that makes one revise ideas on D'Oyly Carte standards. It is a long time since the company had so strong a soprano lead." Other critics agreed: The Times criticised D'Oyly Carte vocal standards in 1968 but called Masterson and Kenneth Sandford "shining exceptions."The Times, 31 January 1968, p. 7 She remained with D'Oyly Carte for five years, where her major roles were Mabel; Josephine in H.M.S. Pinafore; Phyllis in Iolanthe; Lady Psyche, and subsequently the title role, in Princess Ida; Yum-Yum in The Mikado; Elsie Maynard in The Yeomen of the Guard; and Casilda in The Gondoliers. She appeared as Yum-Yum in the company's 1966 film version of The Mikado.Shepherd, Marc. "The 1966 D'Oyly Carte Mikado Film". A Gilbert and Sullivan Discography, 15 April 2009, accessed 16 July 2014 She left the company in 1969 but often returned for guest appearances.
