The Amnesty donation will go towards the Human Rights Action Centre currently being built in Shoreditch, East London (Third Sector, 26 May).
The centre is being billed as a focal point for human-rights activists, which will help to narrow the gap that Amnesty has identified between the numbers of people who support its work, and the numbers that actually take part in campaigns.
As well as housing Amnesty's headquarters, it will serve as a resource base for people working for the human-rights cause.
Amnesty ended a five-year search when it bought the building for £4.6m in November 2002.
A further £3.5m was needed to refurbish the property, and the Roddicks hope that their donation will convince other wealthy benefactors to stump up the remaining £700,000 required.
"I'm not challenging them - challenging is too strong. I'm hoping to cajole them," Anita Roddick told Third Sector.
"My take on it is 'hey come on, why do you want to sit on another beach, why do you want to buy another Lear jet?' It makes me feel alive doing this stuff, and I'm always looking for reasons to feel alive."
Roddick has been campaigning with Amnesty since her teens, and said she chose it as the benefactor of this year's donation because "activism has always been part of my DNA".
"Amnesty is one of the most relevant, life-affirming organisations and it is more of a moral barometer than almost anything else on this planet."
She said the couple knew who future benefactors were likely to be, but the organisations had not yet decided whether they wanted to publicise the fact.
"They are worried people will say 'well they've got enough money now'." But Roddick added that the donations would go to groups dealing with issues surrounding child sweatshop labour and global warming.