The man had gone out to feed the animal on the property at Moyhu, south of Wangaratta, when it attacked the 47-year-old, the ABC reported.
His wife was then attacked when she tried to help.
The ABC has been told the couple’s teenage son hit the deer with a lump of wood to save his mother.
It is believed that the stag responsible was a pet Wapiti bull or red cross that would have been in full rut.
Despite the best efforts from paramedics, the man died at the scene from critical injuries.
The woman suffered life-threatening upper-body and leg injuries and was treated by air ambulance.
She has since been flown to Alfred Hospital in Melbourne in a critical condition.
“Emergency services are on scene at a rural address near Wangaratta after an animal incident which occurred this morning,” Victoria Police said in a statement.
“It’s believed a man and woman were attacked by a deer on their property around 8.20am.
“Both residents suffered critical injuries however the man died a short time later.
“The woman has been airlifted to hospital with life-threatening injuries.
“The investigation is ongoing.”
Ambulance Victoria said the woman suffered upper body and leg injuries and was flown to the Alfred Hospital.
She was reported to be in a serious condition.
Victoria Police confirmed the deer had been killed by officers.