More people will move out of Melbourne to towns like Geelong, Ballarat and Bendigo, the planning department's report predicts.
Victoria's population is likely to reach 10 million people by the middle of the century, with Melbourne swelling to almost 8 million, new planning department figures show.
Melbourne's current population is 4.3 million, while the state has 5.7 million residents.
Victoria in Future, released on Friday by Planning Minister Matthew Guy, shows that 720,000 extra people will live within Melbourne's suburban boundaries by 2031.
The figures also show that the fertility rate will remain constant at 1.8 children per woman, with rates expected to increase in the 30 to 35-year-old age group.
More than half of the regional growth the state will see up until 2051 will come from people moving out of Melbourne to towns like Geelong, Ballarat and Bendigo, the report predicts.
And it says the fastest growing areas of greater Melbourne will be Melton, Wyndham and Melbourne City Council's areas during the next 20 years.
Life expectancy for those born in 2051 is also expected to have increased to 87.6 years for males and 89.9 years for females.
The report was produced to help inform the Napthine government's Plan Melbourne strategy for the city, released last week.
Mr Guy said the Vic-toria in Future report showed the tide had turned on falling fertility rates.
"Since the early 1970s, our fertility rate has been falling and the number of children born every year has remained virtually unchanged," he said. "But now that's turned around, with twice as many babies expected to be born in 2050 than in 2000."
This natural population increase would mean that, as a result of more children being born and a longer life expectancy, there would be an increase of 1.8 million people in Victoria by 2051.
This would account for 40 per cent of the city's total growth, Mr Guy said.
"These projections confirm Victoria is a great place to live," he said. People were choosing to live and raise a family in Victoria "confident of what the future holds", Mr Guy said.
Detailed breakdowns of the projected population growth figures can be found at www.dtpli.vic.gov.au/victoria-in-future-2014.