The Pentagon on Friday said the US Army had agreed to abandon charges of mishandling classified information while Capt James Yee worked at the US Naval base at Guantanamo Bay, Cuba.
"They collapsed. Chaplain Yee has won his case," Yee's civilian lawyer, Eugene Fidell said.
"This represents a long overdue vindication. In our view, he's entitled to an apology and we will be looking forward to receiving one," the lawyer said.
Capt Yee,who also uses the first name Yusuf, was arrested last September as he arrived at a Florida naval base and spent 76 days in military detention.
The US Army accused him in a court document of spying, mutiny, sedition, aiding the enemy and espionage.
In October he was charged with failing to obey orders and particularly for taking classified material to his home.
A Chinese-American, Capt Yee converted to Islam while serving in Saudi Arabia after the 1991 Gulf War.