It follows a £1.5 million commitment in the Borderlands Deal and £5.5m pledged by Community Windpower Ltd.
And the SOSE money will help pay for design and site costs, legal and quantity surveyor fees and the project management.
The Star landmark is proposed to be 40 metres high and will aim to stimulate economic growth by attracting additional visitors to the region.
Welcoming the latest funding, Gretna Landmark Trust chairman Alasdair Houston, said: “The Star of Caledonia is a project of international importance that will be invaluable in promoting regeneration and recovery in the wake of the pandemic by shining a light on Dumfries and Galloway.
“This SOSE funding is a tremendous boost that takes us another step forward in our quest to create a truly fitting landmark at the border between Scotland and England.
“The business case funding will be the key to unlocking £1.5 million which, in addition to the other generous funding pledges, would mean that work could begin on-site within months.”
Pictured are representatives of SOSE, politicians and the Gretna Landmark Trust.
Among them is South Scotland MSP Emma Harper, who said: “The proposal is that the Star of Caledonia will become an iconic Scottish landmark with national and international appeal, located at the entry point to our stunning South West Scotland to be enjoyed by our local communities as well as visitors to the area. It will encourage visitors to enter South Scotland and explore our beautiful borderlands and Dumfries and Galloway.”