Ken Block became the first Fire Rescue Commissioner in mid 2020, when Victoria's country and metropolitan fire services merged.
Mr Block has returned to Canada due to what's been described as significant family health issues and can no longer work in Victoria.
"Mr Block has been instrumental in establishing and leading Fire Rescue Victoria," Emergency Services Minister Jaclyn Symes said.
"He has built a highly professional emergency services agency, bringing professional firefighters together under one organisation with community safety at its core."
Deputy Commissioner Gavin Freeman will act in the top job until a permanent replacement is found.
Mr Block was appointed to the newly-created Fire Rescue Victoria after a tumultuous time for fire services in the state, after years of disputes about the future of the Country Fire Authority.
That organisation is now volunteer-only while professional firefighters are employed by Fire Rescue Victoria.
The organisation is currently dealing with the impact of a cyber attack in late 2022, which temporarily affected phone, email and dispatch systems.
Last month the organisation revealed anyone who ever applied for a job or was employed at the service could have had their personal details stolen and posted to the dark web.
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