Following his early career in the Army (Major), he became a riding instructor, including a spell as instructor to the Olympic gold medal winning team in 1952. His first training licence was as private trainer to Major Lionel Holliday at La Grange Stables in Newmarket, before moving to West Ilsley three years later.
Hern became a St. Leger Stakes specialist, winning the event six times. He produced three Epsom Derby winners in Troy (1979), Henbit (1980) and Nashwan (1989), who also won the 2,000 Guineas and the King George VI & Queen Elizabeth Stakes. Hern trained the legendary Brigadier Gerard who was only beaten once in eighteen races. Other major winners include Sun Princess, Dayjur, Hethersett, Bireme, Bustino, Longboat, Little Wolf, Petoski, Highclere, Provoke, Prince of Dance, Minster Son, Unfuwain, Dunfermline, Cut Above.
In December 1984 Hern was seriously disabled in a hunting accident, after which time he used a wheelchair.
In 1988 he was controversially sacked from his position as trainer for Queen Elizabeth II at West Ilsley by her racing manager 7th Earl of Carnarvon - Hern was recovering from heart surgery at the time. Later a compromise was reached whereby Hern shared the stable with the new incumbent - William Hastings-Bass (later Earl of Huntingdon) for a year before moving to Hamdan Al Maktoum's Kingwood House Stables in Lambourn.
Dick Hern died in 2002 at Oxford, England at age 81.