Philip Hammond called the idea, which was in the Conservative party pre-election manifesto as well as the coalition agreement, 'bizarre'.
Speaking while visiting British projects helping to treat Ebola in Sierra Leone, he said it didn't need to be put in law because the UK was already meeting the United Nations target: "Trying to enshrine it in law - it's a bizarre idea. Somebody says shall we have a law that says you've got to build a building.
"Think about it - in the mean time we built a building. Someone comes along and says now we've built it shall we pass the law which says we've got to do it? We've done it. We're doing it. You don't need a law to say we're doing it."
International development charity Christian Aid is criticising the comments.
Head of Advocacy Laura Taylor told Premier's News Hour she was 'baffled' by what Mr Hammond had to say.
She said: "That promise was made in the Conservative party's manifesto so they were elected on the assumption that they would bring in this bill.
"It just makes sense to see through this promise his party has made particularly at a time when Ebola is happening and there's crises in Syria, Gaza and other parts of the world."
Mr Hammond's also facing criticism from Deputy Prime Minister Nick Clegg.
Speaking on his LBC radio show he said: "I think what is a little bizarre - to put it as diplomatically as I can - is that the Foreign Secretary, a Conservative, should go to Sierra Leone to tear up his own manifesto.
"It was a Conservative party manifesto commitment to legislate on this commitment of devoting 0.7% of our national income."
The Government is yet to act on its promise to introduce it as law however a private member's bill is working its way through parliament.
It's unclear whether it'll be completed before the election in May.
Hear Laura Taylor speaking in full on Premier's News Hour: