Birgit Nilsson (Marta Birgit Svensson) (born May 17, 1918) is a Swedish soprano.

She was born in Västra Karup (near Malmö), Sweden. Her vocal talent was first noticed when she began to sing in her church choir. She studied with Ragnar Blennow in Bastad Joseph Hislop and Arne Sunnegard at the Royal Academy of Music in Stockholm.

She made her operatic debut at the Royal Swedish Opera in 1946 as Agathe in Weber's Der Freischütz with only three days' notice. In 1947, she gained national attention as Lady Macbeth in Verdi's Macbeth at the Royal Opera. Her first important international appearance was in Mozart's Idomeneo at the Glyndebourne Festival in 1951. She first sang Brünnhilde in Munic in 1954.

She made her American debut in 1956 with the San Francisco Opera. In 1959 Nilsson gained North American prominence as Isolde in Wagner's Tristan and Isolde at the Metropolitan Opera in New York City. The same year, she made her Bayreuth debut as Else in Lohengrin and returned regularly until 1970. She has performed at many major opera houses in the world including Tokyo, Paris, Buenos Aires, Chicago, and Hamburg.

She was widely known as the leading Wagnerian soprano of her time, the successor of Kirsten Flagstad, her compatriot, particularly in the role of Brünnhilde. However, she also sang many of the other famous soprano roles, among them Leonore, Aida, Turandot, Tosca, Elektra, and Salome.

An interesting anecdote is told that characterizes her relationship with Rudolph Bing, long-time director of the Metropolitan Opera. When Bing was asked if she was difficult, he reportedly said, "Not at all. You put enough money in, and a glorious voice comes out." And when Miss Nilsson was preparing her taxes and was asked if she had any dependents, she replied, "Yes, just one, Rudolph Bing."

She has made numerous recordings, including a complete Ring cycle as Brünnhilde for Decca. All of her major roles have been recorded.

She married Bertil Niklasson, a veterinary student she had met on a train, in 1948.

The American Scandinavian Foundation has named their prize for promising young American opera singers the Birgit Nilsson Prize.

Her autobiography, Mina minnesbilder, was published in Stockholm in 1977. Nilsson retired from the stage in 1984.