Kempff was born in Jüterbog, Brandenburg, in 1895. He grew up in nearby Potsdam where his father was a royal music director and organist at St. Nicolai Church. His grandfather was also an organist and his brother Georg became director of church music at the University of Erlangen. Kempff studied music at first at the Berlin Hochschule für Musik at the age of nine after receiving lessons from his father at a younger age. Whilst there he studied composition with Robert Kahn and piano with Karl Heinrich Barth (with whom Arthur Rubinstein also studied). In 1914 Kempff moved on to study at the Viktoria gymnasium in Potsdam before returning to Berlin to finish his training.
The pianist Alfred Brendel has written that Kempff "played on impulse... it depended on whether the right breeze, as with an aeolian harp, was blowing. You then would take something home that you never heard elsewhere." (in Brendel's book, The Veil of Order). He regards Kempff as the "most rhythmical" of his colleagues. Brendel helped choose the selections for Phillip's "Great Pianists of the 20th Century" issue of Kempff recordings, and wrote in the notes that he regarded Kempff "achieves things that are beyond him" in his "unsurpassable" recording of Liszt's first Legende, "St. Francis Preaching to the Birds."
When pianist Artur Schnabel undertook his pioneering complete recording of the Beethoven sonatas in the 1930s, he told EMI that if he didn't complete the cycle, they should have Kempff complete the remainder - even though the two pianists took noticeably different approaches to the composer (for example, Schnabel preferred extremely fast or slow tempos, while Kempff preferred moderate ones). Later, when Kempff was in Finland, the composer Jean Sibelius asked him to play the slow movement of Beethoven's 29th Sonata, the Hammerklavier; after Kempff finished, Sibelius told him, "You did not play that as a pianist but rather as a human being."
As a performer he stressed lyricism, charm, and spontaneity in music, particularly effective in intimate pieces or passages. He always strove for a singing, lyrical quality, occasionally slipping into a slight degree of affectation in his phrasing. He avoided extreme tempos and display for its own sake. He left recordings of most of his repertory, including the complete sonatas of Beethoven and Schubert. He performed to an advanced age, often concertizing past his eightieth birthday. He appeared in 1979 with the Berlin Philharmonic, marking an association with them that spanned over sixty years.
As a teacher
In 1924–1929 Wilhelm Kempff took over the direction of the Stuttgart College of Music as a successor of Max Pauer. In 1931 he was co-founder of the Summer courses at Marmorpalais Potsdam. In 1957 Wilhelm Kempff founded “Fondazione Orfeo” (today: Kempff Kulturstiftung) in the south-italian city Positano and held his first Beethoven interpretation masterclass at Casa Orfeo, which Kempff had built especially for this reason. Until 1982 he continued teaching there once a year. After his death in 1991, Gerhard Oppitz taught the courses from 1992-1994 until John O´Conor continued till today. Oppitz and O’Conor had both been outstanding participants of Kempff´s masterclasses and were personally closely connected with Wilhelm Kempff. Other noted pianists to have studied with Kempff include Jörg Demus, Norman Shetler, Mitsuko Uchida, Peter Schmalfuss, Idil Biret and Carmen Piazzini.
A lesser-known activity of Kempff was composing. He composed for almost every genre and used his own cadenzas for Beethoven's Piano Concertos 1-4. His student Idil Biret has recorded a CD of his piano works. His second symphony premiered in 1929 at the Leipzig Gewandhaus by Wilhelm Furtwängler. He also prepared a number of Bach transcriptions, including the Siciliano from the Flute Sonata in E major, that have been recorded by Kempff and others.