The green-and-white Scandinavian-style banner was today formally recognised by the Lyon Court, the heraldic authority for Scotland, after being used by islanders for decades to promote local produce.
The project gained extra significance after island resident Eilidh MacLeod, 14, was among those killed in the Manchester Arena terror attack in May.
The Barra flag was draped on her coffin as she was laid to rest the following month.
Eilidh’s close friend and fellow islander, Laura MacIntyre, was seriously injured in the blast. The 15-year-old returned home in August after treatment in Manchester.
The teenage pair, both pupils at Castlebay Community School, had made the long trip down south to attend an Ariana Grande concert. They had travelled with Eilidh’s mother, who had arranged to meet the girls afterwards.
Barra has a population of around 1,100 and is the second most southerly inhabited isle in the Outer Hebrides.
Philip Tibbetts of the Flag Institute said: “It is wonderful to see the Barra flag achieve official recognition with the Lyon Court, having been used so extensively over the years.
“In this past year Barra has shown the importance that a flag can have for its community - not only as a celebration but also as a symbol to rally around.
“As such it has been both an honour and humbling to have assisted Barra since I was first invited to the island last year.
“I am sure it will serve as a powerful example to the many other communities thinking of developing their own flag to promote their own identity and the patchwork of national heritage.”
Barra follows in the footsteps of South Uist, which became the first island in the Outer Hebrides to have its banner gain official status.
The project was pursued by the isle’s two community councils, after the initial meeting headed by Alasdair Allan MSP.
Northbay community councillor Dolina Manford said: “I am very happy to see that the Barra flag has now received official recognition from the Lord Lyon.
“It has been a long process but now the green and white Nordic cross that has been used in Barra for a number of years is officially registered at the Lord Lyon.”
Mr Allan added: “When I originally held an exploratory meeting on this subject it was felt that recognition of the flag would help to boost the island’s marketing efforts as well as celebrate its unique identity.
“I would like to thank Dolina for her efforts in driving this forward and I look forward to seeing some of the benefits this will bring.”
The Court of the Lord Lyon has the power to authorise community flags and ensure that only one community can use any one design.
Angus MacNeil, MP for Na h-Eileanan an Iar, said: “I’m very pleased that the Barra Isles flag has been approved, with the Nordic cross showing not just the ancestry of the people but the places names of Barra, and the green representing the green of the Barra Isles. This is a fantastic achievement by all those involved.”