Defence Minister Stephen Smith has said the presence of the US military in Australia would "continue to be a force for peace, for security, for stability and for prosperity".
"This is very much an historic day," he told media.
"It is a history day rooted deeply in the history of the US-Australian alliance, going back 60 years."
Mr Smith said the Australian-US relationship would be crucial as the international focus shifts to the Asia-Pacific region with the emerging economies of China, India and Indonesia.
"As the world moves in our direction, Australia has to accommodate to that."
US Ambassador Jeffrey Bleich said the US also recognised the importance of the Asia-Pacific region.
"This is the fastest growing economic area, and we want to ensure it is a peaceful and prosperous area," he said.
Mr Bleich said the increased occurrence of natural disasters in the region would be one challenge where the US military could be of assistance.
"We have to be prepred for every eventuality," he said.
Earlier, Defence Minister Stephen Smith addressed the first contingent of US marines to arrive in Darwin.
The 200-strong Fox Company is the first contingent of 2500 soldiers who will eventually be stationed in Darwin under a bilateral agreement struck by US President Barack Obama and Prime Minister Julia Gillard last year.
Mr Smith said Australians would welcome the presence of marines in Darwin.
"You are here today because more than 60 years ago Australia and the United States forged an alliance, an alliance which has served us well for over 60 years, an alliance forged in the Pacific during World War II in defence of Australia, in defence of the Pacific, in defence of the United States, in defence of democracy and freedom."
"US marines have a fine tradition in the Pacific and a fine tradition in Australia; you are highly regarded and highly respected.
"You are very welcome here."
Troops from the 5th Battalion of the Royal Australian Regiment were present at the ceremony.
Dignitaries in attendance included NT Chief Minister Paul Henderson, US Ambassador Jeffrey Bleich, and Minister for Defence Science and Personnel, Warren Snowdon.