Brown, who has previously talked about his struggles with a stammer, sings lead vocals on the reworked version of fans' favourite Highland Cathedral, which he hopes will rouse their spirits.
He is joined on the recording by Euan Murray, Henry Pyrgos and Matt Scott – the first time Scottish rugby players have collaborated on a single.
Profits from the track, available to download from midnight on Saturday, will be split between three rugby charities: The Bill McLaren Foundation, Hearts and Balls and The Murrayfield Centenary Fund.
The project came about when fans keen to create a new supporters' anthem went to the Scottish Rugby Union with specially written lyrics for the instrumental classic.
Brown said: "I was approached by a group of supporters and they were passionate about it. I was asked if I would like to help. Any excuse to sing."
Agreeing to have his voice blasted across Murrayfield may seem a curious choice for a man who has admitted wincing when watching himself stammer in interviews, but Brown has always found solace in singing.
His gravelly performance of Mustang Sally is said to have become something of a cult favourite in rugby circles, while his dark eyebrows have drawn comparisons to Kelly Jones, lead singer of the Stereophonics.
Asked why he was so relaxed in front of the microphone, Brown said: "That's a very good question, I'm not quite sure. But if you look at another stammerer called Gareth Gates, he went on Pop Idol with a very bad stammer [yet] as soon as he came to sing the song he was absolutely fine."
The charity song was produced by Calum Malcolm – who has worked with Scottish bands including Wet Wet Wet, Simple Minds and Orange Juice – and will be released by Edinburgh label The Music Kitchen. It also features children from 15 schools across Aberdeenshire.
To make it into the top 40, the song must sell about 20,000 copies, while an estimated 40,000 sales are needed to break even and start making money for charity.
The two Scottish rugby fans behind the new lyrics, Simon Paterson-Brown and Chris Thomson, said they were overjoyed with the end result and are crossing their fingers for a chart entrance.
Mr Paterson-Brown said: "The track is a wonderful new vocal version of a superb tune that encompasses all that is best about Scotland and her people.
"As a passionate rugby supporter who knew of Kelly Brown's singing prowess, it was an obvious choice to ask him to record it, with some of his more musical teammates and school children from Aberdeenshire.
With the video being given its first public airing in front of a crowd at Murrayfield, the single could make an entrance in the charts next week."
Brown, who has been picking his team up after defeat to England last weekend, has previously spoken about living in the spotlight with a stammer.
He said last year: "I'm in a fortunate position in that I'm in the public eye. If I can help any stammerers out there, I'm happy to do so. I don't think it should hold somebody back; I certainly tried to make sure it never held me back."