Born near Alexanderplatz in Berlin to a middle-class Jewish family, he began his musical education at the Stern Conservatory at the age of eight, making his first public appearance as a pianist when he was nine; he performed a concerto movement with the Berlin Philharmonic in 1889 and a full concerto with them in February, 1890.
He studied composition at Stern with Robert Radecke, and remained active as a composer until about 1910 (see list of compositions below). But it was hearing a concert in 1889 by the Berlin Philharmonic led by Hans von Bülow, he wrote, that "decided my future. Now I knew what I was meant for. No musical activity but that of an orchestral conductor could any longer be considered by me." He made his conducting début at the Cologne Opera with Albert Lortzing's Der Waffenschmied in 1894. Later that year he left for the Hamburg Opera to work as a chorus director. There he first met and worked with Gustav Mahler, whom he revered and with whose music he later became strongly identified.
In 1896, he was appointed Kapellmeister of the Stadttheater (municipal opera) in Breslau, on the strength of a recommendation from Mahler to the theater's director, Theodor Löwe. However, Löwe required that before taking up this position the young conductor change his last name from Schlesinger which literally means Silesian "because of its frequent occurrence in the capital of Silesia". In a letter to his brother, paraphrased by biographers Erik Ryding and Rebecca Pechefsky, Walter said that he had "suggested several names, which Mahler wrote down and gave to Löwe, who returned the contract with the name Bruno Walter". These biographers add that Walter wrote to his parents that he found that "having to change his name was 'terrible'". They report that Mahler and his sisters "pressed" Walter to make the change of name, and add that contrary to occasional unsubstantiated reports, it "is unknown" whether Löwe's stipulation had anything to do with a desire to conceal Walter's Jewish origins.
In 1897, Walter became Chief Conductor at the municipal opera in Pressburg (now Bratislava). He found the town provincial and depressing, and in 1898 took the position of Chief Conductor of the Riga Opera, Russian Empire. While there, he converted to Christianity, probably Roman Catholicism. In 1899 Walter was appointed music director of the Temeswar, Austria-Hungary (now Timisoara, Romania) Opera, the current Banatul Philharmonic of Timișoara. Walter then returned in 1900 to Berlin, where he assumed the post of Royal Prussian Conductor at the Staatsoper Unter den Linden, succeeding Franz Schalk; his colleagues there included Richard Strauss and Karl Muck. While in Berlin he also conducted the premiere of Der arme Heinrich by Hans Pfitzner, who became a lifelong friend.
In 1901, Walter accepted Mahler's invitation to be his assistant at the Court Opera in Vienna. Walter led Verdi's Aida at his debut. In 1907 he was elected by the Vienna Philharmonic to conduct its Nicolai Concert. In 1910, he helped Mahler select and coach solo singers for the premiere of Mahler's Symphony No. 8. In the following years Walter's conducting reputation soared as he was invited to conduct across Europe in Prague, in London where in 1910 he conducted Tristan und Isolde and Ethel Smyth's The Wreckers at Covent Garden, and in Rome. When Mahler died on May 18, 1911, Walter was at his deathbed. On June 6, he wrote to his sister that he was to conduct the premiere of Mahler's Das Lied von der Erde; he did so in Munich on November 20, 1911, in the first half of an all-Mahler concert (the second half contained Mahler's Symphony No. 2). On June 26, 1912 he led the Vienna Philharmonic in the world premiere of Mahler's Symphony No. 9.
Although Walter became an Austrian citizen in 1911, he left Vienna in 1913 to become the Royal Bavarian Music Director and General Music Director of the Bavarian State Opera in Munich. While there, argue Erik Ryding and Rebecca Pechefsky, "Walter's contribution to the history of Wagner performance was more significant than many realize. The Bayreuth Festival was suspended after 1914 ... and resumed only in 1924. During those nine years, Munich was the centre of authentic Wagner performance; its Prinzregenttheather was closely patterned after the Festspielhaus in Bayreuth, and its National Theatre had seen the world premieres of Die Meistersinger von Nürnberg, Das Rheingold, Die Walküre, and Tristan und Isolde. Walter was the city's music director for most of this period, and he presided over most of the Wagnerian repertoire."
In January 1914, Walter conducted his first concert in Moscow. During the First World War he remained actively involved in conducting, giving premieres to Erich Wolfgang Korngold's Violanta and Der Ring des Polykrates as well as Hans Pfitzner's Palestrina. In 1920, he conducted the premiere of Walter Braunfels' Die Vögel.
In Munich, Walter was a good friend of Cardinal Eugenio Pacelli (later Pope Pius XII). Walter's close friendship with Thomas Mann seems to have begun in Munich by 1914.
Walter ended his Munich appointment in 1922 and left for New York in 1923, working with the New York Symphony Orchestra in Carnegie Hall; he later conducted in Detroit, Minnesota and Boston.
Back in Europe, Walter made his debuts with both the Leipzig Gewandhaus Orchestra and the Royal Concertgebouw Orchestra in 1923, and was Music Director of the Deutsche Oper Berlin (Städtische Oper) from 1925 to 1929. He made his debut at La Scala in 1926, and was chief conductor of the German seasons at Covent Garden in London from 1924 to 1931.
Walter served as Principal Conductor of the Leipzig Gewandhaus Orchestra from 1929 until March, 1933, when his tenure was cut short by the new Nazi government, as detailed below.
In speeches in the late 1920s, Nazi leader Adolf Hitler had complained bitterly about the presence of Jewish conductors at the Berlin opera, and mentioned Walter a number of times, adding to Walter's name the words "alias Schlesinger." When the Nazis took power, they undertook a systematic process of barring Jews from artistic life.
On November 1, 1939, he set sail for the United States, which became his permanent home. He settled in Beverly Hills, California, where his many expatriate neighbors included Thomas Mann.
While Walter had many influences within music, in his Of Music and Making (1957) he notes a profound influence from the philosopher Rudolf Steiner. He notes, "In old age I have had the good fortune to be initiated into the world of anthroposophy and during the past few years to make a profound study of the teachings of Rudolf Steiner. Here we see alive and in operation that deliverance of which Friedrich Hölderlin speaks; its blessing has flowed over me, and so this book is the confession of belief in anthroposophy. There is no part of my inward life that has not had new light shed upon it, or been stimulated, by the lofty teachings of Rudolf Steiner ... I am profoundly grateful for having been so boundlessly enriched ... It is glorious to become a learner again at my time of life. I have a sense of the rejuvenation of my whole being which gives strength and renewal to my musicianship, even to my music-making."
Bruno Walter died of a heart attack in his Beverly Hills home in 1962, but he is buried in the cemetery of Gentilino in Canton Ticino, Switzerland.