Australian Defence Minister Stephen Smith and US ambassador Jeffrey Bleich exchanged diplomatic notes on Thursday in Canberra to formally bring an Australia-US Defence Trade Treaty into effect.
Secretary of State John Kerry said the new treaty deepens the already strong relationship the countries share.
"Today's entry into force of the Defence Trade Co-operation Treaty between the United States and Australia enables American and Australian troops to get the best technology in the fastest way possible," Mr Kerry said in a statement from Washington DC.
"It will expand our reach and help defend our interests around the world."
AAP reports Australia is the second country, after Britain, to secure a similar trade treaty with the United States.
Prior to the treaty, Australian defence companies had to negotiate complex US defence export procedures and apply for approval on every occasion. Companies can now obtain a global authorisation.
"Australia is already a significant defence trade partner of the United States and one of our closest allies and this treaty deepens our relationship even further," Mr Kerry said