Hempel was born at Chelsea, Middlesex, on 28 August 1777, and showing very early indications of musical talent was placed under the tuition of his relative, Augustus F. C. Kollmann, organist and composer.
He made rapid progress, and at the age of eight performed during the service at the king's German chapel, St. James's.
For the use of his pupils in 1822 he printed an Introduction to the Pianoforte, comprising Elementary Instruction, with a series of Practical Lessons.
Hempel also became known as a poet in 1822 by his work entitled The Commercial Tourist, or Gentleman Traveller, a satirical poem in four cantos.
The West Briton states that he died at his son's residence, Wolsingham Place, Kennington Road, London, on 14 March 1855; but a more trustworthy source, the registrar-general's return, says that after acting as a banker's clerk he died in the workhouse, Prince's Road, Lambeth, London, on 14 March 1855.