The future opera star's father, August Lehmann, was a singer while her mother, Maria Theresia Löw (1809 - 1885), was a soprano of Jewish origin. Her first lessons were from her mother, who had been a prima donna under Spohr at the Cassel opera. After singing small parts on the stage, Lehmann made her proper debut in 1870 in Berlin as a light soprano in Meyerbeer's Das Feldlager in Schlesien. She subsesequently became so successful that she was appointed an Imperial Chamber Singer in 1876.
Lehmann sang in the first Bayreuth Festival in 1876, performed in London in 1884, and appeared at the New York Metropolitan Opera in 1885-1890. Together with her Met colleagues Fischer, Alvary, Brandt, and Seidl, she helped to popularise Wagner's music in America. By remaining in America beyond the leave granted her by the Berlin Opera, she faced a ban following her return to Germany. After the personal intervention of the Emperor, the ban was lifted.
She appeared at London's Royal Opera House, Covent Garden, in 1899 and sang in Paris and Vienna in 1903 and 1909 respectively. In 1905, she sang at the Salzburg Festival, later becoming the festival's artistic director. Lehmann was also renowned as a Lieder singer. She continued to give recitals until her retirement from the concert stage in the 1920s.
Her mature voice, of splendid quality and large volume, gained for her the reputation of being not only one of the greatest Wagnerian singers of her day but also an ideal interpreter of Bellini's Norma and the operatic music of Mozart. She was considered unsurpassed in the rôles of Brünnhilde and Isolde but sang an astonishingly wide array of other parts. Indeed, across the span of her career, she performed 170 different parts in a total of 119 German, Italian and French operas. She was also a noted voice teacher. Among her pupils were the famous sopranos Geraldine Farrar and Olive Fremstad.
In 1888, she married the tenor Paul Kalisch.
Lehmann founded the International Summer Academy at the Mozarteum in Salzburg in 1916. The academy's curriculum concentrated on voice lessons at first but it was extended later to include a wide variety of musical instruction.
The Lilli Lehmann Medal is awarded by the Mozarteum in her honour. Her voice can be heard on CD reissues of the recordings which she made prior to World War One. Although past her peak as an operatic singer when she made these records, they still impress.