Kate Grimwade, an integral part of Godolphin's Australian racing stable for the past 12 months, will leave the global operation's Melbourne yard.
Grimwade will return to England after arriving in Australia last August to run Godolphin's Carbine Lodge at Flemington for head trainer James Cummings.
She has cited family reasons for leaving.
During Grimwade's time in Victoria, Godolphin Australian-trained stars such as Hartnell, Best Of Days, Alizee, Avilius and Microphone scored important Melbourne wins.
"I've loved my time in Melbourne looking after a great group of people and horses contributing to a very successful season for the team," she said.
"I'm passionate about the sport and I look forward to the next part of my career back in the UK."
Reg Fleming, a long-time Melbourne stable foreman for legendary trainer Bart Cummings, will coordinate the early spring campaigns of Godolphin's Victorian team.
A Godolphin statement said a long-term decision on Grimwade's replacement would be made in the coming weeks.
Cummings-trained Godolphin runners will be out in force for the PB Lawrence Stakes meeting at Caulfield on Saturday.
Stable stalwart Hartnell will lead the contingent as he tries to win the weight-for-age Lawrence for a second time.
A nine-year-old, Hartnell starts his latest Australian having not raced since finishing third in Winx's farewell race - the Queen Elizabeth Stakes at Randwick in April.