Robertson, number two in the agency to MD Kate Hawker, will remain with F-H's London office until 'at least July' before moving.
Hawker said she was not on the hunt for a replacement in London 'as Mandi is remaining with us as a consultant'.
It is not yet decided whether Robertson, who has worked at The Remedy for around four years and as Hawker's deputy for two, will work from home or be based in F-H's Melbourne office.
The Remedy has 15 staff and clients include Pfizer and Japanese drugs firm Takeda.
- Separately, two Fleishman-Hillard UK healthcare staff have quit to join Edelman's healthcare team in London.
Senior account manager Louise Pontifex is leaving after two and a half years, while account manager Sarah Hoffman is to exit after five and a half years. Both will join Edelman within a fortnight as senior account managers.
F-H's recently arrived director of pan-European healthcare PR Patrick Krol said he was recruiting to replace the pair.