Peter Snowden has shocked racing circles by announcing he will quit as head trainer of Darley's Australian thoroughbred stable.

Snowden will leave Sheikh Mohammed's southern hemisphere racing enterprise at the end of the Sydney autumn carnival in April.

A Darley Australia statement confirmed Snowden and his son Paul, who oversees the operation's Melbourne stable, will set up their own training partnership.

Henry Plumptre, managing director for Darley Australia, said a transition plan had been put in place and there would be no rush to name Snowden's replacement.

Snowden said Wednesday's announcement would not have an impact on Australia's biggest racing stable in the short-term.

"I'm still here for six months so nothing changes," Snowden told AAP.

In a prepared statement, Snowden said he was proud of what he had achieved at Darley and looked forward to bowing out with a flurry of winners.

"Sheikh Mohammed has provided me with an amazing opportunity and I will be forever grateful," he said.

"When the time comes we will deal with the farewells but for now my focus is on producing results for Darley."

Snowden has made a great start to the new racing season, plundering four Group One races during spring carnivals in Sydney and Melbourne.

His spring haul included the Caulfield Guineas with Long John, the Flight Stakes and Thousand Guineas with Guelph and the Spring Champion Stakes with Complacent.

Plumptre expects Snowden's legacy at Darley to be strong well beyond his departure.

"Peter's record speaks for itself and we have been very fortunate to have him as our head trainer," Plumptre said.

"His legacy will continue as we benefit from the offspring of champion colts Sepoy, Helmet and Denman.

"Peter has already amassed a formidable record for Sheikh Mohammed and Darley. He plans to add to that record between now and the end of the Sydney autumn carnival."

Snowden was a long-serving foreman to John Hawkes under the Woodlands Stud banner.

He was promoted to head trainer for the Ingham family racing operation in November 2007 after Hawkes stepped down to go into a training partnership with his sons.

In May the following year, Woodlands sold its breeding and racing empire to Sheikh Mohammed and Snowden stayed on as head trainer for Darley.

Some of the best gallopers Snowden has trained under the Darley banner include Forensics, Denman, Sepoy and Guelph.

Darley galloper Chiaroscuro scored at Canterbury on Wednesday, keeping Snowden in second place behind Chris Waller in the Sydney trainers' premiership.