Johann Sebastian Bach's professional life developed through a succession of church, court and civic appointments. After early work in Weimar, he became organist at Arnstadt in 1703 and Mühlhausen in 1707. He played, maintained instruments and directed music. His visit to Lübeck to hear Dieterich Buxtehude broadened his experience but also brought conflict over an extended absence. Returning to Weimar in 1708, he served as court organist and later concertmaster, composing organ works and cantatas while studying and adapting music by other composers.

In 1717 Bach entered Prince Leopold's service at Köthen as Kapellmeister. The court's musical priorities encouraged instrumental writing, including concertos, chamber music and works for solo strings and keyboard. The Brandenburg Concertos were presented to the Margrave of Brandenburg in 1721. The first book of The Well-Tempered Clavier, completed in 1722, joined systematic exploration of keys with practical teaching and compositional invention. These works combine German, Italian and French styles through contrapuntal mastery.

Bach became Thomaskantor in Leipzig in 1723, directing music for principal churches and teaching at the Thomasschule. The demanding position generated cycles of cantatas for the church year and major sacred works, including the St John and St Matthew Passions. Their performance depended on rehearsing singers and instrumentalists and negotiating the resources supplied by civic and ecclesiastical authorities. Disputes over duties and musical standards repeatedly complicated his employment. He also directed the Collegium Musicum, providing a setting for secular performances and keyboard concertos beyond his church responsibilities.

Later projects included the Goldberg Variations, the Musical Offering and the unfinished Art of Fugue. The Mass in B minor gathered and reworked material into a large Latin setting that exceeded ordinary Lutheran liturgical needs. Bach's household was also a centre of musical instruction, and several sons pursued distinguished careers. He died in Leipzig in 1750 after declining health and unsuccessful eye treatment. His reputation as a keyboard master survived even when much of his vocal music circulated less widely. Nineteenth-century performances, scholarship and publication expanded awareness of his achievement. His career united the practical demands of employed musicianship with works that became central to the study and performance of European music.