From 1963 to 1966, Blegen sang with the Nuremberg Opera, and at the Vienna State Opera from 1968 to 1970, making her debut there as Rosina in Il Barbiere di Siviglia. She made a successful appearance at the Santa Fe Opera in August 1969, in the role of Emily in Menotti’s satirical opera Help! Help! The Globolinks!, which was written especially for her. In January 1979, she made her Metropolitan Opera debut in New York as Papagena in The Magic Flute, becoming one of the Metropolitans's leading sopranos, singing roles such as Zerlina, Marzelline, Gilda, Sophie, Blondchen, Adele, Oscar, and Juliette. In 1975, she made her first appearance at London’s Covent Garden, and in 1977 in the Paris Opera.