In 1790, Horsley became the pupil of the pianist and composer Theodore Smith (c. 1740-1810), who taught him sufficiently well to obtain the position of organist at Ely Chapel, Holborn, in 1794.
Besides holding this appointment he became the organist of Belgrave Chapel, Halkin Street, in 1812 and of the Charter House in 1838.
There are five surviving piano sonatas, composed between 1812–17, of which Nicholas Temperley and Leanne Langley particularly highlight No.
[5] The Horsley family were friendly with Mendelssohn and, according to L T C Rolt, were the first to hear his music for A Midsummer Night's Dream, played by him on the piano at their home at No 1 High Row (now 128 Church Street) in Kensington.
Horsley's eldest daughter Mary Elizabeth (born 1813) married the engineer Isambard Kingdom Brunel.