Researcher David Leishman said evidence shows a drink called IRONBREW was first launched by a New York firm in 1889.
It wasn’t until the summer of 1898 that A.G.Barr brought their IRON BREW to the market before officially launching their recipe in 1901.
Mr Leishman said the drink became “Scottish through branding and advertising rather than being invented in Scotland”.
And he also claimed an English firm invented the iconic strongman image on the can which later became known as the iconic “Highland athlete”.
Mr Leishman, originally from East Kilbride and who teaches at Grenoble Alpes University, said the drink was sold in the US under the brand of IRONBREW and was described as the “The Ideal American drink”.
He admitted he was apprehensive about revealing his findings.
He said: “In my mind, I had always thought that the drink was invented in Scotland.
“But, following my research, I find it quite heartening that IRN-BRU has become Scottish through branding and advertising rather than being invented in Scotland.
“I was a bit apprehensive about announcing some of these findings to AG BARR plc, particularly the fact that the strongman was invented by an English firm.
“Robin Barr and marketing director Jonathan Kemp were extremely helpful though, allowing me access to the company’s own archives, answering questions and undertaking their own research as a result of my findings.”
IRONBREW was described as “The Ideal American drink” by manufacturers and chemicals firm Maas & Waldstein.
The firm trademarked the name and successfully sued copycat brands, but it faded from view in the 1920s, with the exception of a few regional markets.
IRONBREW claimed to have serious health benefits for the US market.
But following the 1911 Pure Food and Drug Act, its makers were no longer able to boast of benefits within their advertising.
The original American IRONBREW is also thought to have been a dark colour with a vanilla taste - similar to arch rival Coca-Cola.
In the UK, the first company to sell the flavour and essence to bottlers was London-based Stevenson & Howell which launched its product in the summer of 1898.
To advertise the drink, which they called Iron Brew, they registered a strongman holding aloft a glass of the beverage surrounded by weights and dumbbells as a trademark.
This featured on bottle labels and advertising that Stevenson and Howell supplied bottlers with and the liquid was the more familiar orange colour that we know today.
While AG Barr said it made its own original recipe, the strongman was unknowingly adopted by the company.
The figure later became identified with the Highland Games athlete Adam Brown.
Barr’s own IRN-BRU was on sale as early as 1898, three years earlier than the official launch date.
Mr Leishman added: “In recent decades Barr’s have never claimed to be the inventor of Iron Brew drinks but they were surprised that they did not come up with the strongman image.
“They had no idea that the Stevenson and Howell strongman even existed.
“But I wanted to dispel some of the urban myths surrounding the origins of the drink to better understand how it became associated with Scottish identity.
“My father was from Falkirk and was a big local history enthusiast with a special interest in Barr’s, so I suppose the idea for this project came from him.”
A spokesman for A.G. Barr said that despite there being a number of different versions over the years no one has come close to matching the Barr recipe.
He said: “There’s no doubt there have been Iron Brews in the past, but for us there is only one real IRN-BRU.
“That’s the IRN-BRU still made by us today, according to the long-standing Barr secret recipe.”