Opening a meeting in the Oval Office, Obama said the leaders planned to discuss the anti-Islamic State operation, as well as broader counterterrorism efforts in the Middle East and Southeast Asia.
The president noted Australia is a key contributor to the coalition, with the second-largest force of ground troops in Iraq behind the United States.
"They have been a consistent and extraordinarily effective member of the coalition," Obama said.
Australia has six jet fighters based in Dubai flying missions against Islamic State targets in Iraq and Syria. It also has soldiers in non-combat roles in the Iraqi capital of Baghdad.
Turnbull said his visit had included productive meetings with Defense Secretary Ash Carter. He said he looked forward to working more closely with US intelligence officials on counterterrorism efforts aimed at curbing the Islamic State's recruitment and communications online.