Committee for Melbourne chief executive Andrew MacLeod said a doubling of Melbourne's population over the next 50 years was a "normal" rate of growth as its population surges towards 8 million by 2060.
At the current growth rate, Melbourne will overtake Sydney as Australia's biggest city in the 2030s.
Demographer Bernard Salt said Melbourne had the capacity to double in size.
"A city of eight million may seem shocking now but it will be no bigger than London or Paris are currently," he said.
"And it will rebalance Melbourne with most of the future growth expected to be in the north and west of the city.
"At the moment Melbourne stretches 50km to the east to Pakenham but only 30km to the west to Melton."
A population of eight million would stretch the city's boundaries to Wallan in the north and Werribee in the west.
Moving jobs out of the CBD was the key to maintaining Melbourne's liveability, Mr Salt said.
Six new "central activities districts" have already been designated at Box Hill, Broadmeadows, Dandenong, Footscray, Frankston and Ringwood.
Mr Salt said this would breathe life into suburbia, allowing people to spend less time commuting and more time with their families.
Mr MacLeod said the key to maintaining Melbourne's position as one of the world's great cities would be an increase in medium density housing in outer suburbs.
A spokesperson for Planning Minister Justin Madden said plans were being drawn up for about 600,000 new homes across the city.
"The Urban Growth Boundary was recently expanded to release enough land for more than 20 years - enough for 134,000 new homes," the spokesperson said.
"And there is significant capacity for more housing in Melbourne's existing suburbs, such as the re-use of old industrial sites.
"It is vital to draw on this capacity when planning for Melbourne's growth."