The Australian government had hoped to send the first group of asylum seekers to the Manus Island processing centre last month.
But the first transfer was postponed as discussions were held with Islanders to assure them local workers and businesses will be involved.
Mr Marles, who travelled to Port Moresby this week, says the first asylum seekers will arrive soon.
"The timing is measured in days, there will be transfers in the coming days," he said.
The Governor of Manus Island says the Papua New Guinean government has given Australia permission to send asylum seekers to the island for processing at any time.
Charlie Benjamin says Port Moresby had asked the Canberra to delay sending the first group of asylum seekers until it had clarified the opportunities for locals to provide services to the centre, and given details on development assistance plans.
On Wednesday, however, Mr Benjamin said those issues were no longer a problem.
"The final details are still [being] worked on," he told the Pacific Beat program.
"There is a team that will be going to Manus to assess the type of assistance that would be given and the type of request that we have given to them to assist to know exactly how much it might cost.
"But overall, I think we're quite happy with what is happening."