She was born as Tini Rössler to a German-speaking family in the town of Lieben, near Prague, now in the Czech Republic but then part of the Austrian Empire. Her father Hans Rössler was a shoe maker; while previously serving as an Austrian cavalry officer, he had been stationed in northern Italy (then an Austrian protectorate), where he met and married Charlotte Goldman, with whom he returned to Lieben. When Ernestine was three years old, the family moved to Verona. In 1866, at the outbreak of the Seven Weeks War, the family moved to Prague, where she was schooled at the Ursuline Convent. At war's end, the Roesslers moved to Podgrozj, near Krakow. The family moved again to Graz when Tini was thirteen. Here she met Marietta von LeClair, a retired opera singer who agreed to give her voice lessons. In 1877 she made her first professional performance, in Beethoven's Ninth Symphony in Graz, appearing with soprano Maria Wilt.

Tini made her operatic debut at Dresden's Royal Opera House on October 15, 1878 as Azucena in Il Trovatore.

In 1882 she married Ernest Heink, secretary of the Dresden Opera, with whom she had four children; this violated the terms of their contracts, and both were abruptly terminated from their positions. Heink took a job at the local customs house and was soon transferred to Hamburg. Ernestine remained in Dresden to pursue her career, and eventually rejoined her husband when she secured a position at the Hamburg Opera.

Ernest Heink was again thrown out of work when Saxons were banned from government positions, and departed to Saxony to find work. Ernestine, pregnant, did not follow him; they were divorced in 1893. That year she married actor Paul Schumann, with whom she had three more children. The second marriage lasted until Paul Schumann's death in 1904.

Her breakthrough into leading roles was provided when prima donna Marie Goetze argued with the director of the Hamburg opera. He asked Ernestine to sing the title role of Carmen, without rehearsal, which she did to great acclaim. Goetze, in a fit of pique, cancelled out of the role of Fides in La Prophete, to be performed the following night, and was again replaced by Ernestine. Schumann-Heink replaced Goetze as Orturd in Lohengrin the following evening, again without rehearsal, and was offered a ten-year contract.

She performed with Gustav Mahler at the Royal Opera House, Covent Garden, London, and became well known for her performances of the works of Richard Wagner at Bayreuth, singing at the Bayreuth Festivals from 1896 to 1914.

She first sang at the Metropolitan Opera in New York City in 1898, and performed with the Met regularly thereafter for decades.

Schumann-Heink made the first of her many phonograph recordings in 1900.

In 1905 she married William Rapp, Jr., her manager. They divorced in 1915.

In the midst of a legal battle in Germany over her late husband's estate, she filed U.S. naturalization papers on February 10, 1905, which became final on March 3, 1908. She and her new husband lived on Caldwell Mountain, near Montclair, New Jersey in her “Villa Fides” from April 1906 to December 1911; she then moved to 500 acres (2 km²) of farm land (located just outside of San Diego, California, and purchased by her in January 1910), where she would live for most of her life.

In 1909 she created the role of Clytemnestra in debut of Richard Strauss' Elektra, which she said she had no high opinion. Strauss, for his part, was not entirely taken by Schumann-Heink; according to one story, during rehearsals he told the orchestra "Louder! I can still hear Mme. Schumann-Heink!"

During World War I she toured the United States raising money for the war effort, although she had relatives fighting on both sides of the war - including her son August Heink, a merchant marine who joined the German submarine service, and step-son Walter Schumann and sons Henry Heink and George Washington Schumann, all in the American Navy.

In 1926 she first sang Silent Night (in both German and English) over the radio for Christmas. This became a Christmas tradition with US radio listeners through Christmas of 1935.

Her last performance at the Met was in 1932.

In her later years she had a weekly radio program.

Ernestine Schumann-Heink died of leukaemia.