Béla Bartók was born in the small Banatian town of Nagyszentmiklós in Austria-Hungary (now Sânnicolau Mare, Romania) on March 25, 1881. He displayed notable musical talent very early in life: according to his mother, he could distinguish between different dance rhythms that she played on the piano even before he learned to speak in complete sentences. By the age of four, he was able to play 40 pieces on the piano and his mother began formally teaching him the next year. Béla was a small and sickly child and suffered from a painful chronic rash until the age of five. In 1888, when he was seven, his father (the director of an agricultural school) died suddenly. Béla's mother then took him and his sister, Erzsebet, to live in Nagyszőlős (today Vinogradiv, Ukraine) and then to Pozsony (German: Pressburg, today Bratislava, Slovakia). In Pozsony, Béla gave his first public recital at age eleven to a warm critical reception. Among the pieces he played was his own first composition, written two years previously: a short piece called "The Course of the Danube". Shortly thereafter László Erkel accepted him as a pupil.

Bartók studied piano under István Thomán, a former student of Franz Liszt, and composition under János Koessler at the Royal Academy of Music in Budapest from 1899 to 1903. There he met Zoltán Kodály, who influenced him greatly and became his lifelong friend and colleague. In 1903, Bartók wrote his first major orchestral work, Kossuth, a symphonic poem which honored Lajos Kossuth, hero of the Hungarian Revolution of 1848. The music of Richard Strauss, whom he met in 1902 at the Budapest premiere of Also sprach Zarathustra, was very influential on his early work. When visiting a holiday resort in the summer of 1904, Bartók overheard the eighteen year old nanny, Lidi Dósa from Kibéd in Maros-Torda in Transylvania sing folk songs to the children under her care. This sparked his life-long dedication to folk music. From 1907 his music also began to be influenced by Claude Debussy, whose compositions Kodály had brought back from Paris. Bartók's large-scale orchestral works were still in the style of Johannes Brahms and Richard Strauss, but also around this time he wrote a number of small piano pieces which show his growing interest in folk music. The first piece to show clear signs of this new interest is the String Quartet No. 1 in A minor (1908), which contains folk-like elements.

In 1907, Bartók began teaching as a piano professor at the Royal Academy. This position freed him from touring Europe as a pianist and enabled him to stay in Hungary. Among his notable students were Fritz Reiner, Sir Georg Solti, György Sándor, Ernő Balogh, Lili Kraus, and, after Bartók moved to the United States, Jack Beeson and Violet Archer.

In 1908, inspired by both their own interest in folk music and by the contemporary resurgence of interest in traditional national culture, he and Kodály travelled into the countryside to collect and research old Magyar folk melodies. Their findings came as a surprise: Magyar folk music had previously been categorised as Gypsy music. The classic example of this misconception is Franz Liszt's famous Hungarian Rhapsodies for piano, which were based on popular art-songs performed by Gypsy bands of the time. In contrast, the old Magyar folk melodies discovered by Bartók and Kodály bore little resemblance to the popular music performed by these Gypsy bands. Instead, they found that many of the folk songs are based on pentatonic scales similar to those in Oriental folk traditions, such as those of Central Asia and Siberia.

Bartók and Kodály quickly set about incorporating elements of real Magyar peasant music into their compositions. Both Bartók and Kodály frequently quoted folk songs verbatim and wrote pieces derived entirely from authentic folk melodies. An example is his two volumes entitled For Children for solo piano containing 80 folk tunes to which he wrote accompaniment. Bartók's style in his art music compositions was a synthesis of folk music, classicism, and modernism. His melodic and harmonic sense was profoundly influenced by the folk music of Hungary, Romania, and many other nations, and he was especially fond of the asymmetrical dance rhythms and pungent harmonies found in Bulgarian music. Most of his early compositions offer a blend of nationalist and late Romanticism elements.

In 1909, Bartók married Márta Ziegler. Their son, Béla II, was born in 1910. In 1911, Bartók wrote what was to be his only opera, Bluebeard's Castle, dedicated to Márta. He entered it for a prize awarded by the Hungarian Fine Arts Commission, which rejected it out of hand as un-stageworthy. In 1917 Bartók revised the score in preparation for the 1918 première, for which he rewrote the ending. Following the 1919 revolution, he was pressured by the government to remove the name of the blacklisted librettist Béla Balázs (by then a refugee in Vienna) from the opera. Bluebeard's Castle received only one revival, in 1936, before Bartók emigrated. For the remainder of his life, although he was passionately devoted to Hungary, its people and its culture, he never felt much loyalty to its government or its official establishments.

After his disappointment over the Fine Arts Commission prize, Bartók wrote little for two or three years, preferring to concentrate on collecting and arranging folk music. He collected first in the Carpathian Basin (the then Kingdom of Hungary), where he notated Hungarian, Slovakian, Romanian and Bulgarian folk music. He also collected in Moldavia, Wallachia and in 1913 in Algeria. However, the outbreak of World War I forced him to stop these expeditions, and he returned to composing, writing the ballet The Wooden Prince in 1914–16 and the String Quartet No. 2 in 1915–17, both influenced by Debussy. It was The Wooden Prince which gave him some degree of international fame.

Raised as a Roman Catholic, Bartók had by his early adulthood become an atheist and considered the existence of God as undecidable and unnecessary. He later became attracted to Unitarianism and publicly converted to the Unitarian faith in 1916. His son later became president of the Hungarian Unitarian Church.

He subsequently worked on another ballet, The Miraculous Mandarin influenced by Igor Stravinsky, Arnold Schoenberg, as well as Richard Strauss, following this up with his two violin sonatas (written in 1921 and 1922 respectively) which are harmonically and structurally some of the most complex pieces he wrote. The Miraculous Mandarin, a sordid modern story of prostitution, robbery, and murder, was started in 1918, but not performed until 1926 because of its sexual content. He wrote his third and fourth string quartets in 1927–28, after which his compositions demonstrate his mature style. Notable examples of this period are Divertimento for String Orchestra BB 118 (1939) and Music for Strings, Percussion and Celesta (1936). The String Quartet No. 5 (1934) is written in somewhat more traditional style. Bartók wrote his sixth and last string quartet in 1939, the sadness of which has been related to the death of Bartók’s mother and the looming war in Europe.

Bartók divorced Márta in 1923, and married a piano student, Ditta Pásztory. His second son, Péter, was born in 1924.

In 1936 he travelled to Turkey to collect and study folk music. He worked in collaboration with Turkish composer Ahmet Adnan Saygun mostly around Adana.

In 1940, as the European political situation worsened after the outbreak of World War II, Bartók was increasingly tempted to flee Hungary. He was strongly opposed to the Nazis and Hungary’s siding with Germany. After the Nazis had come to power in Germany, he refused to give concerts there and broke from his German publisher. His views caused him a great deal of trouble with the establishment in Hungary. Having first sent his manuscripts out of the country, Bartók reluctantly emigrated to the U.S. with Ditta Pásztory. They settled in New York City. After joining them in 1942, Péter Bartók enlisted in the United States Navy. Béla Bartók, Jr. remained in Hungary.

Bartók never became fully at home in the U.S. He initially found it difficult to compose. Although well-known in America as a pianist, ethnomusicologist and teacher, he was not well known as a composer and there was little interest in his music during his final years. He and his wife Ditta gave concerts. Bartók, who had made some recordings in Hungary also recorded for Columbia Records after he came to the U.S; many of these recordings (some with Bartók's own spoken introductions) were later issued on LP and CD.

For several years, supported by a research fellowship from Columbia University, Bartók and his wife worked on a large collection of Serbian and Croatian folk songs in Columbia's libraries. Bartók's difficulties during his first years in the US were mitigated by publication royalties, teaching and performance tours. While their finances were always precarious, it is a myth that he lived and died in abject poverty and neglect. There were enough supporters to ensure that there was sufficient money and work available for him to live on. Bartók was a proud man and did not easily accept charity. Though he was not a member of ASCAP, the society paid for any medical care he needed in his last two years and Bartók accepted this.

The first symptoms of his leukemia began in 1940, when his right shoulder began to show signs of stiffening. In 1942 symptoms increased and he started having bouts of fever but the disease was not diagnosed in spite of medical examinations. Finally, in April 1944, leukemia was diagnosed but by this time little could be done.

As his body failed, Bartók's creative energy reawakened and he produced a final set of masterpieces, partly thanks to the violinist Joseph Szigeti and the conductor Fritz Reiner (Reiner had been Bartók's friend and champion since his days as Bartók's student at the Royal Academy). Bartók's last work might well have been the String Quartet No. 6 but for Serge Koussevitsky's commission for the Concerto for Orchestra. Koussevitsky's Boston Symphony Orchestra premièred the work in December 1944 to highly positive reviews. Concerto for Orchestra quickly became Bartók's most popular work, although he did not live to see its full impact. He was also commissioned in 1944 by Yehudi Menuhin to write a Sonata for Solo Violin. In 1945 Bartók composed his Piano Concerto No. 3, a graceful and almost neo-classical work and he began work on his Viola Concerto. He had not completed the scoring at his death.

Bartók died in New York from leukemia (specifically, of secondary polycythemia) on September 26, 1945 at age 64. His funeral was attended by only ten people, including his friend the pianist György Sándor. Bartok's body was initially interred in Ferncliff Cemetery in Hartsdale, New York, but during the final year of communist Hungary in the late 1980s, his remains were transferred to Budapest for a state funeral on July 7, 1988 with interment in Budapest's Farkasréti Cemetery.

He left his Third Piano Concerto almost finished at his death. For the Viola Concerto he only left the viola part and sketches of the orchestra part. Both works were later completed by his pupil, Tibor Serly. György Sándor was the soloist in the first performance of the Third Piano Concerto on February 8, 1946. The Viola Concerto was revised and polished in the 1990s by Bartók's son, Peter, and this version may be closer to what Bartók may have intended.

There is a statue of Béla Bartók in Brussels, Belgium, near the central train station in a public square, Spanjeplein-Place d'Espagne. Another statue stands in London, opposite South Kensington Underground Station. Still another is in front of one of the houses that Bartók owned in the hills above Budapest, which is now a museum.