Sugar kelp - common in Japanese cooking - will be hand-dived from the seas around the new Isle of Harris distillery and infused into the spirit.
The final recipe is still being perfected and the gin does not yet have a name but distillery bosses believe they have found the perfect Hebridean twist on a traditional spirit.
A botanist was tasked with discovering the special ingredient and chose seaweed over island plants such as heather and bog myrtle.
The experts say it will bring a saltiness to the gin, but also, surprisingly, a sweet flavour.
The first batch, which will cost around £35 a bottle and be 45 per cent proof, will be ready by around the end of September.
It will come four years ahead of the distillery's main product - a £400 a bottle single malt whisky which will be named named "The Hearach" - the Gaelic word for an inhabitant of Harris.
Traditionally crofters depended in the nutrient rich and readily available sea plant to fertilise the soil.
In recent years it has enjoyed a renewed popularity finding its way into products like water biscuits, health drinks, sea salt and even shortbread.
Now it has found a new use in the islands first distillery which could help the spirit stand out in the thriving Scottish gin market.
We dry the kelp, it is only used in minute quantities, it is very powerful, said Simon Erlanger, managing director of the distillery.
The recipe is a lot more than sugar kelp, but that is the local ingredient.
He continued: The only way to harvest sugar kelp is to hand dive for it - we can only take it in a small quantity.
Asked when the gin will be ready to taste he said: We are still to finish the construction. We expect it will be the end of September.
The distillery website explains: "We were keen to discover which botanicals our islands flora could bring to the fore.
"Our fragile island environment may not lend itself well to the commercial gathering of ingredients but with care and attention we hoped to find something special.
"Sugar kelp is a true Hebridean seaweed found in underwater forests all around the island."
As expected for a seaweed, it holds a salty flavour element but crucially, as indicated by the name, it is also sweet due to the presence of a substance called mannitol (named after the biblical foodstuff manna).
The gin market is booming with the value of gin sold in the UK increasing from 70m to 408m over the last two years.
The sales of premium gins, which are becoming a speciality of several traditional Scottish whisky distilleries, are said to be up 26.5 per cent on last year.
Alessandro Borelli, Chief Gin Concierge at the Sheraton Grand Spa Hotel in Edinburgh, explained that his bar currently stock 16 Scottish gins.
But he is excited to try the new Hebridean seaweed concoction.
He said: "I'm curious, I want to try it," he said. "Lots of distillers are looking for a subtle taste already. Blackwoods use botanicals from Shetland for example."
Speaking about what flavour people can expect from the kelp he said: "It is dried before and infused in the base spirit. It gives the gin a saltiness and a spiciness as well."
He continued: "The water is very important. Water is 50 per cent of the gin. If it is soft or peaty water it make a big difference. Its like a whisky - peat would add a smoky taste.
He added that Scottish craft gins were growing in popularity: "The new Scottish gins are doing great. The gin industry in Scotland, the distillation knowledge is immense."
