Johann Christian Bach (September 5, 1735—January 1, 1782), the eleventh son of Johann Sebastian Bach, was born at Leipzig, Germany. His father, and possibly also Johann Elias Bach, trained young Johann Christian in music. It is believed that Book II of Johann Sebastian's The Well Tempered Clavier was written and used for Johann Christian's instruction. Johann Christian served as copyist to his father. On the death of his father in 1750, Johann Christian became the pupil of his brother Carl Philipp Emanuel Bach at Berlin.
In 1754 he went to Italy where he studied counterpoint under Giovanni Battista Martini, and from 1760 to 1762 held the post of organist at Milan cathedral, for which he wrote two Masses, a Requiem, a Te Deum and other works. Around this time he converted from Lutheran to Roman Catholic.
He was the only one of Johann Sebastian's sons to write opera in Italian, starting with arias inserted into the operas of others, then pasticcios, the Teatro Regio in Turin commissioned him to write Artaserse, an opera seria that was premiered in 1760. This led to more opera commission, leading to commissions for the King's Theatre in London, an invitation in 1762 invitation to go there, where he spent the rest of his life. The Milan Cathedral kept his position open, hoping he'd return.
For twenty years he was the most popular musician in England, his dramatic works, produced at the King’s theatre, were received with great cordiality. The first of these, Orione, was one of the first few musical works to use clarinets. He was appointed music master to the Queen, and his duties included giving music lessons to her and her children, and accompanying on piano the King playing flute. His concerts, given in partnership with Abel at the Hanover Square rooms, soon became the most fashionable of public entertainments.
Johann Christian Bach died in London on the first day of 1782. Wolfgang Amadeus Mozart said in a letter to his father Leopold that it was "a loss to the musical world".
Although Bach's fame declined in the decades following his death, his music still showed up on concert programmes in London with some regularity, often coupled with works by Haydn. In the 20th century, scholarly work on the life and music of Bach and his father led to renewed appreciation.
He is of some historical interest as the first composer who preferred the pianoforte to the older keyed-instruments. Johann Christian's early music shows the influence of his older brother Cal Philipp Emanuel, while his middle period in Italy shows the influence of Martini.
A full account of J. C. Bach’s career is given in the fourth volume of Burney’s History of Music.
There are two others named Johann Christian Bach in the Bach family tree, but neither was a musician.