Update: Labour & the Lib Dems overwhelming won the vote, with just seven Tories voting against.
All of Westminster's three main parties promised it in their 2010 manifestos – but it's taken a single backbencher to give their pledge to lock down 0.7% of Britain's gross national income on aid spending a chance of becoming law.
Michael Moore, the former Liberal Democrat Cabinet minister, is the MP in question. The coalition somehow didn't find time to get this job done. So he's using his chance at a private member's bill to wrap up this unfinished business himself.
"In this situation there is no awkward choice between altruism and national interests – development makes a difference to us all," he writes for Politics.co.uk today.
"This is about leadership – the chance to set the clearest example to other wealthy countries to persuade them to join us in the commitment."
Development NGOs are falling over themselves with enthusiasm for what would become an unprecedented commitment.
It's taken over half a century to get this far. The World Council of Churches first made the call for a 0.7% commitment in 1958.
Right now the UK is the only country in the G7 to have spent this much of its income on helping out others overseas. Making it permanent, the charities insist, isn't something we should regret.
"This year alone, UK aid means five million children have gone to school, around 20 million people have access to clean water and 48 million children received polio vaccinations," says Diane Sheard, UK director of development charity One.
Tearfund's chief executive Matthew Frost points out 61% of adults support this much spending – and a fifth think it is too low.
"To tackle poverty the debate must move on to the structural causes - climate change and resource scarcity, corruption, trade failures and conflict," he says.
"This bill is a welcome opportunity to move the debate on."
World Vision UK's chief executive Justin Byworth puts it more simply: "Now is our chance to keep our promise to the poor."
Despite all this support, though, there is still a very strong chance Moore's chance will not make it through parliament.
While the Conservatives, Liberal Democrat and Labour party frontbenches are all happy to support it, there are a number of Tory backbenchers who could exploit the weaknesses of private member's bills and scupper this legislation.
Peter Bone, for example, has already gone on the record making clear he wants this bill to fail.
"I can quite understand why a Liberal Democrat would want to go ahead with that because they don't believe in financial management and are keen to get rid of taxpayers' money," he said earlier this year.
"But the issue goes back to how does a percentage of gross national income ever relate to need? We need to have overseas aid based on need.
"What happens [with a fixed target] is you get close to the end of the financial year and lots of money gets doled out by the overseas aid department because they have to reach the target."
Today, the second reading of the international development (official development assistance target) bill, will be Bone's first chance to ruin it. Liberal Democrat sources indicate they expect he will be joined by around 15 others – more than enough to cause huge headaches for Moore and co.
The biggest challenge is getting the closure motion – which ends debate on the bill and thus allows it to move forward in the legislative process – agreed to. If a single MP shouts 'object' when this is moved, the Commons votes. Under its standing orders, at least 100 MPs are required.
They should be alright. The 'turn up, save lives' campaign has been seeking pledges from MPs to show up in the Commons today and get the bill through. It's currently displaying 101 names on its website.
So then the bill will move off to committee, where filibustering is possible. The real danger, though, is when it returns to the Commons for report stage. There is no defence here against those MPs determined to 'talk the bill out'. It becomes a matter of priorities then. Is this legislation really important enough that the malcontents can be faced down?
For Labour and the Lib Dems, the answer is probably 'yes'. But there is a serious question-mark over the Conservative party's collective will. They support international development spending, yes. But they also support another private member's bill competing with Michael Moore's for limited parliamentary time. Under the terms of the Parliamentary Act, his EU referendum bill only needs to get through the Commons unamended for it to become law.
Which bill, when it comes to it, will the Tories prefer? The same goes for their right-wing backbench grumblers, too. If they really want a referendum that badly, will they be prepared to let Moore's sail through unobstructed in order to give as much time as possible to their much-prized referendum legislation?