Dean Holland was riding three-year-old Headingley in the first race at Donald, a town northwest of Melbourne, when he was thrown to the ground as his horse hit the inside rail.
On-course paramedics immediately went to Holland's help but he died from his injuries aged 34, Racing Victoria said.
Another rider involved in the incident was not hurt, nor were their horses. The meeting was abandoned.
"It was a tragic accident at Donald today and we are all deeply shocked and saddened that Dean has passed away as a result of injuries sustained in the fall," said Racing Victoria chief executive Andrew Jones.
"Dean was a gifted lightweight rider who won over 1,000 races and was highly respected by his peers."
Holland won his first Group 1 race in the 2010 Schweppes Oaks, before claiming his second aboard filly In Secret at Flemington last month.
Victorian Jockeys Association chief Matt Hyland said he was "incredibly saddened by the loss of our colleague and friend".
More than 880 jockeys have died in falls since racing began in Australia in 1847, according to the National Jockeys Trust, with about 200 injured each year.
