Harold Badger was so small as a schoolboy that he was constantly advised to seek a career as a jockey. He took this advice to heart, and leaving school at the age of 14 in 1922, he was soon apprenticed at Flemington to Richard Bradfield.
It was his light weight that led to Badger's first major success, when Bradfield took him to South Australia where he won the 1925 Adelaide Cup on Stralia carrying 6st 10lb (43 kg). Granted his senior jockey's licence in 1927, he moved to Adelaide as stable jockey for trainer Alf Williams. Badger was an immediate success, winning the jockeys' premiership in his first season.
Returning to Melbourne in 1930, Badger rode for the powerful Lou Robertson stable and for Frank Musgrave, trainer of Ajax. With Ajax's regular rider, Maurice McCarten unavailable, Badger took the mount in the 1937 Victoria Derby and rode Ajax into second place, beaten by the narrowest of margins. Badger and Ajax went on to form one of the great partnerships in turf history – Badger riding Ajax in 37 races for 30 wins, five seconds, and two thirds.
Success on Ajax put Badger in demand with leading Victorian owners and trainers, and he won his first Victorian jockeys' premiership in the 1938-39 season. Further premierships came in 1939-40, 1940-41, 1941-42, 1942-43, and 1947-48. Badger's big race successes included two Caulfield Cups, Moonee Valley, Adelaide and Brisbane Cups, two Doncaster Handicaps, two Epsom Handicaps, two Cox Plates, two Newmarket Handicaps, and three Futurity Stakes.
Harold Badger was inducted into the Australian Racing Hall of Fame in 2009.