David Miliband has praised the coalition for its "remarkable" achievement of keeping a promise to spend 0.7% of Britain's GDP on foreign aid.
The former Labour foreign secretary, who now runs the International Rescue Committee development charity in New York, said David Cameron and Nick Clegg were right to have "stuck to their guns" on the commitment in the face of opposition.
Miliband also told an audience at the World Affairs Council in California on Tuesday evening that he had decided to take up the post in America as he felt his career in British politics had reached a "dead end".
Yesterday the government confirmed it would lend its support to a backbench Private Member's Bill that would enshrine the aid commitment in law.
The prime minister made achieving the United Nations spending target of 0.7% a key part of his Tory de-toxification strategy while in Opposition. In 2010 the Conservatives and Lib Dems also agreed to make it the law in the coalition agreement, a move that has the support of the Labour Party.
However increasing spending on foreign aid has proved controversial with a substantial number of Tory MPs, who question why, at a time of austerity, money is being spent abroad rather than in the UK. Cameron's decision to back a bill put forward by the Lib Dem former coalition Scottish secretary Michael Moore puts him on a collision course with his backbenchers.
Miliband told his American audience last night: "In the UK, foreign aid has become a bipartisan issue and raising foreign aid has become a bipartisan issue. In the US foreign aid is 0.2% of national income, in UK it's 0.7%, these are relatively small sums compared to the big sums spent on health, education etc."
"To the extent that the Conservative government that succeeded the government I was part of, even when they were slashing budgets left, right and centre on domestic policy, they carried on raising the international development budget which is very remarkable," he said. "Fair do's to them."
"I am very happy to say, to applaud, that they have stuck to their guns," Miliband added. "They haven't gone back on their comment to raise foreign aid to 0.7% and to keep it there. That is a huge sign of progress."
The IRC works with refugees and internally displaced people in crisis hit countries across the world, including Syria. Miliband said the criticism that foreign aid was just throwing "good money after bad" was wrong. "It's not true to say that it's not worth thrown the money at it because it won't be well spent," he said.
Miliband stood down form parliament last year after losing the bitter battle with his brother Ed to become leader of the Labour Party. Asked why he had chosen to take up the post at the IRC in New York, Miliband told his American audience "the electorate of the UK had some say in that" but made no mention of his attempt to become Labour leader.
"The government I was part of lost an election in 2010 so I became an opposition backbencher. And if you've been in high office you feel a sense of impatience to try to learn the lessons and to make use of your experience," he said.
Miliband added: "The more I thought about it the more I felt like I was at a dead end in British politics."
Ed Miliband has been under pressure in recent weeks following a series of critical comments from veteran Labour politicians as well as from within his own shadow cabinet.
The nervousness on the Labour benches has increased as the party's poll lead has narrowed ahead of the 2015 election. One survey showed that voters would be more likely to vote for a Labour government in 2015 were David, rather that Ed, were leader.