Johann Sebastian Bach was born in Eisenach, Thuringia. He was the youngest child of Johann Ambrosius Bach, an organist, and Maria Elisabetha Lämmerhirt Bach. One uncle, Johann Christoph Bach (1645–93), was especially famous and introduced him to the art of organ playing. Bach was proud of his family's musical achievements, and around 1735 he drafted a genealogy, "Origin of the musical Bach family," printed in translation in The Bach Reader. Bach married his second cousin Maria Barbara Bach in 1707. Maria died in 1720, and Bach married Anna Magdalena Wilcke in 1721. Although Bach had twenty children, only seven survived infancy

Bach's mother died in 1694, and his father eight months later. The young Bach probably witnessed and assisted in the maintenance of the organ music. Two of them—Wilhelm Friedemann Bach and Carl Philipp Emanuel Bach—became important composers in the ornate Rococo style that followed the Baroque.

(1703–08)

In January 1703, shortly after graduating, Bach took up a post as a court musician in the chapel of Duke Johann Ernst in Arnstadt. The Bach family had close connections with this oldest town in Thuringia, about 180 km to the southwest of the edge of Weimar. Strong family connections and a musically enthusiastic employer failed to prevent tension between the young organist and the authorities after several years in the post. This well-known incident in Bach’s life involved his walking some 400 kilometres ( 250 mi) each way to spend time with the man he probably regarded as the father-figure of German organists. The trip reinforced Buxtehude’s style as a foundation for Bach’s earlier works, and that he overstayed his planned visit by several months suggests that his time with the old man was of great value to his art. In 1706 he moved to Mühlhausen, and four months after arriving at Mühlhausen, he married his second cousin from Arnstadt, Maria Barbara Bach.

(1708–17)

After barely a year at Mühlhausen, Bach left to become the court organist and concert master at the ducal court in Weimar, a far cry from his earlier position there. The large salary on offer at the court and the prospect of working entirely with a large, well-funded group of professional musicians may have prompted the move. It was there that the two musically significant sons were born—Wilhelm Friedemann and Carl Philipp Emanuel Bach. Bach’s position in marked the start of a sustained period of composing keyboard and orchestral works, in which he had achieved the technical proficiency and confidence to throw together all the types of music that he knew in what ever way he wanted. Bach started transcribing the ensemble concertos of Vivaldi for harpsichord and organ. Bach was particularly attracted to the Italian solo-tutti structure, in which one or more solo instruments alternate section-by-section with the full orchestra throughout a movement. In Mühlhausen, he had the opportunity to play and compose for the organ, and to perform a varied repertoire of concert music with the duke’s ensemble. A master of contrapuntal technique, Bach’s steady output of fugues began in . The largest single body of his fugal writing is Das wohltemperierte Clavier . It is made of 48 preludes and fugues, one pair for each major and relative minor key.

(1717–23)

Bach began once again to search out a more stable job that was conducive to his musical interests. Prince Leopold of Anhalt-Cöthen hired Bach to serve as his Kapellmeister (director of music). Prince Leopold, himself a musician, appreciated Bach’s talents, paid him well, and gave him considerable latitude in composing and performing. However, the prince was Calvinist and did not use elaborate music in his worship; thus, most of Bach’s work from this period was simple. On July 7, 1720, while Bach was abroad with Prince Leopold, tragedy struck: his wife, Maria Barbara, the mother of his first 7 children, died suddenly, ending a large part of his life.

(1723–50)

In 1723, Bach was appointed Cantor of Thomasschule, as well as Director of Music in the principal churches in the town. This was a prestigious post in the leading mercantile city in Saxony. In return for agreeing to Bach’s appointment, the City-Estate faction was granted control of the School, and Bach was required to make a number of compromises with respect to his working conditions. Some of the compromises were that Bach’s job required him to instruct the students of the Thomasschule in singing, and to provide weekly music at the two main churches in Leipzig, St Thomas's and St Nicholas's. Bach had assembled a huge repertoire of church music for ’s two main churches from this agreement. In the words of Christoph Wolff, assuming the directorship was a shrewd move that 'consolidated Bach’s firm grip on Leipzig’s principal musical institutions’.Bach's appointment as court composer appears to have been part of his long-term struggle to achieve greater bargaining power with the Leipzig Council. Although the church mass that Bach wrote was probably never performed during the composer’s lifetime, it is considered to be among the greatest choral works of all time.

In 1747, Bach went to the court of Frederick II of in , where the king played a theme for Bach and challenged him to improvise a fugue based on his theme. Bach improvised a three-part fugue on ’s pianoforte, then a novelty, and later presented the king with a Musical Offering which consists of fugues, canons and a trio based on the "royal theme", nominated by the monarch.

 

Shortly after this, Bach began to loose his sight, and struggled with his work more. But the final work Bach completed was a chorale prelude for organ, dictated to his son-in-law, Johann Altnikol, from his deathbed.

Bach’s works are indexed with BWV numbers, an initialism for Bach Werke Verzeichnis (Bach Works Catalogue). The catalogue is organised thematically, rather than chronologically: BWV 1–224 are cantatas, BWV 225–249 the large-scale choral works, BWV 250–524 chorales and sacred songs, BWV 525–748 organ works, BWV 772–994 other keyboard works, BWV 995–1000 lute music, BWV 1001–40 chamber music, BWV 1041–71 orchestral music, and BWV 1072–1126 canons and fugues.

Bach wrote many works for the harpsichord, some of which may also have been played on the clavichord.

The pieces were intended by Bach for instructional purposes. Among Bach’s lesser known keyboard works are seven toccatas (BWV 910–916), four duets (BWV 802–805), sonatas for keyboard (BWV 963–967), the Six Little Preludes (BWV 933–938) and the Aria variata alla maniera italiana (BWV 989).

Bach wrote music for single instruments, duets and small ensembles. Bach's works for solo instruments – the six sonatas and partitas for violin (BWV 1001–1006), the six cello suites (BWV 1007–1012) and the Partita for solo flute (BWV 1013) – may be listed among the most profound works in the repertoire. Bach also composed a suite and several other works for solo lute.

Bach's other large work, the Mass in B minor, was assembled by Bach near the end of his life, mostly from pieces composed earlier (such as cantata BWV 191 and BWV 12). The easy listening Bach's music and its use in advertising also contributed greatly to Bach's popularity in the second half of the twentieth century. Jazz musicians have also adopted Bach's music, with Jacques Loussier, Ian Anderson and Uri Caine among those creating jazz versions of Bach works.

. Today the "Bach style" continues to influence musical composition, from hymns and religious works to pop and rock. The Bach Society was founded in 1850 to promote the works, publishing a comprehensive edition over the subsequent half century.

Thereafter Bach’s reputation has remained consistently high. Some of the greatest composers since Bach have written works which explicitly pay homage to him.