Development agencies have welcomed the Chancellor's Budget confirming 0.7% of national income will be spent on international aid.
Christian Aid said it was a "historic achievement" on aid.
"Today, a 40 year-old promise to the world's poorest was finally delivered," said Christian Aid director Loretta Minghella.
"We congratulate the Government for ensuring that - even in challenging economic times – this country has done the right thing by the hundreds of millions of women and men around the world living in poverty."
Tearfund advocacy director Paul Cook said the aid budget was the answer to years of prayer, although he added that a lot more needed to be done to eradicate extreme hunger completely.
"Having a percentage commitment to aid was an idea put forward by the church more than fifty years ago and the UK signed up to the 0.7% promise in 1970, so this has been a long time coming," he said.
"Eventually, we should work towards a world where aid budgets aren't needed any more because we have together tackled corruption, helped people to adapt to climate change and created long-term sustainable growth."
World Vision chief executive Justin Byworth said the Government had demonstrated "real leadership" on aid and maintained the UK's status as a world leader in international development despite considerable opposition.
"We understand that the UK is facing its own economic challenges but in a world where one in eight children will go to bed hungry tonight we must keep our own challenges in perspective," he said.
"Setting aside a tiny amount of our budget is not only the right thing to do, it's the smart thing to do because we know that aid works. It has already helped save five million children's lives a year."
However there was disappointment that the Budget will do little to stamp out tax avoidance. Christian Aid had wanted the Government to require multinationals to reveal the tax avoidance schemes they are using in the developing world.
The aid agency estimates developing nations are losing around $160bn a year due to tax dodging by multinationals, more than they receive in aid from wealthy countries.
Ms Minghella said the Budget was a "missed opportunity" to help poor countries collect more of the tax they are owed.
"The Prime Minister's and Chancellor's pronouncements on tax dodging have so far been commendable," she said.
"Now we look forward to the Government leading ambitious global action against tax dodging at the G8 in June.
"That would show that, building on its aid credentials, the UK continues to do the right thing and the smart thing, for people living in poverty around the world."