Ackté studied first with her mother, Emmy Achté, who was the principal soprano of the Helsinki Opera at the time, and made her début there in 1893. The next year she entered the Paris Conservatoire, studying under Edmond Duvernoy and Alfred Girodet, and on 8 October, 1897, she appeared at the Paris Grand Opéra as Gounod's Marguerite. During her studies in France she changed the spelling of her last name.
After Paris, Ackté spent six years touring Europe. Her success led to an engagement at the Metropolitan Opera from 1904 to 1906, where her roles included Marguerite and Juliet in Gounod's operas, and Wagner's Eva, Elsa and Elisabeth. After returning to Europe, in 1907, she sang with Van Dyck's company at Covent Garden, and in the same year at Leipzig gave her first performance as Richard Strauss's Salome, the role for which she became most known for. She sang it also in the British première in 1910 and was recognized especially for performing the Dance of the Seven Veils herself.
She gave up international performances in 1913, and the later part of her career Ackté spent mostly in Finland. In 1911 she helped to found the "Kotimainen Ooppera" (from 1914 the Finnish Opera, and from 1956 the Finnish National Opera), together with Edvard Fazer and Oskar Merikanto, and for one year (1938–9) she became its director.
She wrote the libretto for the opera Juha, set by both Aarre Merikanto and Leevi Madetoja. Jean Sibelius dedicated his tone poem "Luonnotar" to Ackté, and she premiered the work in 1913. She performed for the last time in Finland in 1920. She wrote two autobiographical books, Muistojeni kirja (1925) and Taiteeni taipaleelta (1935).