His comments come in the wake of a planned Supreme Court challenge by Papua New Guinea's opposition leader Belden Namah over the legality of the centre.
Mr Namah says the processing centre is illegal because PNG's constitution only allows people to be detained if they've been charged with a criminal offence.
But Attorney-General Kerenga Kua says the asylum-seekers have effectively consented to being held in a processing centre.
"When they left the shores of their own country, they understood fully well the kind of processing they would have to put through in order to be formally, officially approved as refugees," he said
Mr Namah will file two challenges - one to return the asylum seekers currently in the centre to Australia, and a second to declare the centre unconstitutional and have it removed.
He says he respects the Australian Government's desire to tackle the continuing flow of people-smuggling boats into Australian waters, but he says the law is the law.
"It's important that I take this action is that just to show that our constitution is still supreme," he said.
The Prime Minister Peter O'Neill has said the processing centre is being run in accordance with PNG's laws.
He told local media Mr Namah's court action was a joke that would make a mockery of the country's standing as a regional leader.
In 2005, a plan to have 160 Australian Federal Police officers walk the beats with their PNG counterparts collapsed after the Supreme Court ruled the immunity from prosecution granted to the Australian police was unconstitutional.