A £20 million fundraising campaign is under way after the renowned Grade A-listed building was hit by a blaze last month.
Investigators have yet to state what started the fire which destroyed around 10 per cent of the structure, including the unique library.
The drive to restore the Mackintosh to its former glory has drawn support from former student Peter Capaldi and Mackintosh fan Brad Pitt.
Chief Secretary to the Treasury Danny Alexander said it was only right that “a beautiful building of international importance” received government funds to aid its recovery.
He said: “The Glasgow School of Art is one of Glasgow’s great institutions. The response to the fire from people across the world has been phenomenal.
“I am delighted to be able to announce that the UK Government will be providing £5 million to the Mackintosh Appeal to help the GSA recover and then continue to thrive.
“It is a beautiful building of international importance, so it is right that the UK Government should make a contribution to its restoration.
“We will work with The Glasgow School of Art to ensure that the funding is provided at the most appropriate time to meet their needs.”
GSA director Professor Tom Inns said: “We are determined to restore the building to its former glory, as the inspirational home for the GSA’s creative talent and for the delight of visitors from across the UK and the world.
“The UK Government’s support will help us enormously in our efforts to rebuild, and to ensure we can continue to operate at the highest level internationally, bringing the UK’s creative talent to the world and allowing the world to understand the unique contribution of Mackintosh.”
The Scottish Government has previously said it will match-fund up to £5 million to support the restoration.
Students affected by the fire will also receive up to £750,000 to help them create works to replace those that were lost.