Provisional figures from the Office for National Statistics showed that aid improved by 30.5% in 2013, increasing the total given to poor countries and multinational agencies from 2012's £8.8 billion to £11.4 billion last year.
It took the total as a proportion of gross national income from 0.56% to 0.72%. The UN general assembly first set the 0.7% target in 1970, but few rich countries have hit it in the decades since.
The coalition Government confirmed a promise first set by the previous Labour administration in 2004 to reach it by 2013.
But the pledge has been controversial, some Conservative MPs urging Prime Minister David Cameron to redirect some of the aid cash to other priorities.
The executive director of the Overseas Development Institute thinktank, Kevin Watkins, said: "This is a fantastic achievement reached with cross party co-operation that puts Britain in a leadership position over the greatest challenge facing humanity."
Diane Sheard, UK director of the One campaign, said: "The British people can be proud that we have kept our promise to the poorest people in the world.