On television his most famous role was Doc Morrisey in The Fall and Rise of Reginald Perrin and The Legacy of Reginald Perrin, alongside Sue Nicholls. He also played the recurring character Sir Ralph Shawcross in the roaring twenties sitcom You Rang, M'Lord?, in an ensemble cast which included Paul Shane, Jeffrey Holland, Angela Scoular and Donald Hewlett.
His extensive career began in theatre in Bournemouth and encompassed more than sixty films, and numerous television appearances, including: Shadow Squad, Emergency-Ward 10, Z Cars, No Hiding Place, Dixon of Dock Green, The Avengers, The Lotus Eaters, Crown Court, Clayhanger, The Duchess of Duke Street, Love Among the Artists, Rings on Their Fingers, Leave It to Charlie, Last of the Summer Wine, Oh Happy Band, Hi-De-Hi!, The Box of Delights, Terry and June, Miss Marple, My Husband and I, Woof! and Agatha Christie's Poirot.
Horsley's last credit was a 1997 television adaptation of Rebecca. He died in 2014, aged 93.