"While the C-17 may not prove to be the best solution for New Zealand, we owe it to ourselves to look at it seriously while we can," he said.
The Defence Ministry has been told to replace its five Hercules C-130s - some of which are nearly 50 years old - and two Boeing 757s before 2020.
Mr Brownlee cited New Zealand's work in the Antarctic and the Pacific Islands as reasons for new airlift options.
The C-17 is capable of landing on shorter runways, which is required in some Pacific nations where New Zealand has a role in providing humanitarian support.
It can fly faster and further than the Hercules, which means that unlike the C-130s it can turn around near Antarctica if the weather changes dramatically. A Hercules is unable to turn around once within two hours of Scott Base, which means it sometimes has to land in dangerous conditions.
Labour defence spokesman Phil Goff said the C-17 deserved serious consideration as a replacement for the Hercules.
"The disadvantage New Zealand has with a small budget is that we have to make a single piece of equipment do a number of jobs," Mr Goff said.
But the Labour MP had concerns about timing because the C-17 would cease production in 2015.
This meant that if New Zealand wanted the aircraft it might need to order it quickly and bring forward capital expenditure of hundreds of millions of dollars.
Some MPs and experts did not believe the C-17 would be a good buy for New Zealand.
New Zealand First defence spokesman Ron Mark said that the NZDF did not need the expensive C-17s because most of its day-to-day work involved short-distance missions.
He said if New Zealand wanted to take large numbers of troops a longer distance, it should be able to call on "the club" - Prime Minister John Key's description of its US, Canadian and Australian allies.
Victoria University Centre for Strategic Studies senior fellow Peter Greener said the C-17s were not an adequate replacement for the Hercules and Boeing 757s because they could not provide "tactical" airlift, which could include landing on unsealed runways in a disaster zone.
Aviation overhaul
To be replaced before 2020:
5x Lockheed Hercules C-130H, produced 1954-1996, capable of tactical airlift (shorter-range transport of troops and cargo, landings on unsealed runways). Used by US, British, Canadian, NZ forces.
2x Boeing 757, produced 1981-2004, used for delivering equipment, medical evacuation, troop movements, and VIP transport. Used by commercial airliners and converted for use by RNZAF.
Possible replacements
Boeing C-17 Globemaster III, produced 2001-2015, capable of strategic airlift (long-distance transport of troops and cargo). Used by US, British, Australian, Indian forces. Cost $250m + up to $150m in support and infrastructure
Lockheed Hercules C-130J,
produced 1996-present, upgraded version of the C-130s owned by the RNZAF. Cost $90-$100 million not including support costs.