The ship was released by authorities in Tripoli late on Friday and made contact with an Italian naval vessel taking part in the NATO-led blockade of Libyan waters, Mario Mattioli, chairman of the operator Augusta Offshore said.
"We are very happy that the crew has been released. The last month has been a very uncertain time for us and even more for the crew and their families," he said in a statement.
The Asso 22, a supply vessel which had been working for a client of Italian oil group Eni (ENI.MI), is crewed by eight Italians, two Indians and a Ukrainian.
It was detained on March 19, shortly before western aircraft began imposing a no-fly zone on Libya to prevent forces loyal to Muammar Gaddafi from harming civilians.