Stewart, whose career spans 25 years working at festivals including Glastonbury and the Big Chill, as well as at Green Man, said she was "surprised and thrilled" to receive the accolade from the UKFA.
"I became involved in festivals when they were counter cultural events sometimes even illegal," she added. "They are now a major driver of British culture and international image. I am very proud of the UK festival industry and my future hope is that this hard won heritage is protected and their future diversity is guaranteed from threats of homogenisation."
Stewart's career added an international role when she became a research consultant to the British Council, and commercial arm of the Foreign Office, through which she undertook official visits to China, Serbia, Brazil and India between 2004 and 2010.
She added: "Creating festivals which celebrate difference, and stimulate the inquisitive in a welcoming and comfortable environment is what I strive to do. Any success I have had or contribution I have made to the festival industry has been with the support of the many friends and family who have worked with me over the years, and I would like to dedicate this award to them."
In 2010, she was recruited as a panel member of the Welsh Assembly Creative Industries Advisory Board, and last year she produced Wales' contemporary music programme for the Cultural Olympiad London 2012 Festival.
Carwyn Jones, the First Minister of Wales, said: "I am pleased to congratulate Fiona on this well-deserved honour. Despite her busy schedule Fiona has worked closely with the Welsh government over the last three years as part of the creative industries sector panel, for which she has our thanks.
"Fiona is to be congratulated for the way she has led the development of Green Man as a thought-provoking and original brand."
Stewart will be handed the outstanding achievement award at a ceremony at the Roundhouse in Camden this evening, following a day-long conference focusing on the industry.
James Drury, UKFA director, said: "Fiona's dedication to not only her own events, but the industry as a whole, is inspirational. She is generous with her expertise and that spirit of willingness to share knowledge is something we can all learn from."
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