Following a new deal with npower, the UK's largest electricity supplier, any energy the stadium uses will be purchased from renewable and sustainable sources, such as wind farms and hydroelectric power stations.
Paul Sergeant, Millennium Stadium chief executive said: "The Millennium Stadium took drastic steps in the New Year towards making a firm commitment to looking after our environment.
"We are now in a position at the stadium to start addressing pressing issues about energy sources and usage. Like thousands of others, I never thought energy saving applied to me but we have a responsibility for our children to start taking steps to save our planet. The Millennium Stadium has recently been voted the most iconic building in Wales, so what better place to start?
"With over a million fans visiting the stadium each year the move to go green is extremely important. We hope that this move inspires other stadia across Wales to convert to renewable energy."
Today's announcement will have a real impact on levels of CO2 emissions caused by the stadium's energy consumption. Each year, the stadium uses enough electricity to power approximately 1,900 homes - caused by the running of the floodlights, the retractable roof, all six restaurants, fifteen public bars, twenty-three food and drink service points, the heating, all fifteen escalators, the media centre and all the technology including the two giant screens (equivalent in size to 600 domestic television sets).
Steve Fitzsimons, sales manager for npower business, commented: "We are delighted to help the Millennium Stadium go green. It seems particularly fitting as so much of the renewable energy npower generates comes from Welsh sources. Not only did we open the UK's first major offshore wind farm off the coast of North Wales but we also have seven onshore wind farms and six hydro stations in Wales.
"In all, npower's installed conventional and renewable energy generation in Wales supplies the equivalent of around one-third of its electricity needs."
npower also offers its residential customers a renewable energy product, npower juice, which matches consumer consumption with energy generated from renewable sources at no extra cost.