The Harbours Masterplan aims to improve key sites over the next 20 years, including creating a £116m deep water quay at Scapa.
Scapa Flow is the largest natural deep-water harbour in the northern hemisphere.
It is hoped the scheme could be funded from the Islands Growth Deal as well as from private businesses.
Those behind the plans say up to 100 jobs could be created as well as marine industry jobs at sea and onshore.
Initial investment would see £115.7m spent on the Scapa project, £52.8m spent at Hatston Pier, £39.9m spent at Kirkwall Pier, £15.2m for Scapa Pier and £800,000 spent at Stromness.
The Scapa Deep Water Quay would be a completely new development and would support the energy sector, such as maintenance of vessels and dealing with wind farm components.
The Stromness site would be devoted to capitalising on the increasing popularity of the cruise ship industry in Orkney, with further scope to develop other harbours on the island.
"We've done an outline business case, which conservatively suggests another 115 new jobs for the county," said harbour master Jim Buck. "Those are good, long-term jobs."
He said that offered "generational change".
The development of sites will be split into two phases.
It is hoped phase one will have construction completed on projects within five years.
Council leader James Stockan said: "This is a business proposition - it's not pouring government money in or pouring Orkney money in. It's only going to be used if the business justifies the spend.
"We know that harbour jobs have huge spin off for everybody else on the islands, and that's the way we can make the money circulate."
He added: "We had two world wars, we've had an oil industry that's been with us for 40 years, and we have a pristine environment.
"It's really important that we look after the environment of Scapa Flow so that it's left in very good condition for future generations."