The investor, who is reportedly Belgian, has pledged to store $1 billion in US dollars in deposits on the island.
"The investor has promised to transfer the money in two equal tranches from banks in Brussels and Luxembourg," the minister, Ravi Karunanayake was quoted by the news agency as saying.
"Instead of going for bonds and other borrowing, we are permitting it to take place," he added.
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The country's finances have been precarious over recent months as the rupee has remained low and the Sri Lankan government is forced into borrowing in order to tackle a large deficit in the budget.