Jefferson was born in Penrith and worked as travelling head lad to Gordon W. Richards between 1968 and 1981.
He began training in 1981 and registered his first winner in a bumper at Perth in September of that year.
He continued to train from stables at Norton, North Yorkshire until his death.
[1] Jefferson's most notable successes were gained by Dato Star, who won the Champion Bumper in 1995 and the Christmas Hurdle in 1999.
[2] Jefferson also trained winners in Flat racing, winning the Zetland Stakes in 1983 with High Debate.