Dumfries and Galloway Council and Stena Line have entered into a partnership with the McKinney Group.
It has agreed to bring forward detailed proposals for the regeneration of the East Pier - owned by Stena Line - for new retail, leisure and housing.
Councillor Colin Smyth said the announcement was "another positive step forward" for the town.
"The council has already invested around £4m to develop Agnew Park, the West Pier and sailing facilities as part of the overall vision for the waterfront," he said.
"The redevelopment of the East Pier through private sector investment is the crucial next step for Stranraer.
"We will also continue discussions with the Scottish government to seek support to enable the plans to become a reality."
Speaking on behalf of Stena Line Ports Ltd, Les Stracey said the company was delighted to have reached a "significant milestone".
Billy McKinney, of the McKinney Group, added: "We are delighted to have entered into an agreement with the partners.
"From the outset we recognised the potential for this project to be transformational for Stranraer and the south west of Scotland.
"We aim to work with Stena Line and the council to bring forward proposals that will match the aspirations of the local community and create new growth opportunities for Stranraer."
A preferred bidder has been selected to take forward a potential £50m Stranraer waterfront investment plan.