The former Prime Minister told Sky News that the UK's 0.7 percent commitment said something really great about Britain. Mr Cameron also stated that Britain was breaking a promise to the poorest people and the poorest countries in the world.
The former Prime Minister said: "I think it is a very sad moment, it is not just that we are breaking a promise to the poorest people and the poorest countries in the world that we made and a promise that we do not have to break.
"That 0.7 percent commitment really said something about Britain.
"It said that we were going to spend that money helping the poorest countries.
"It said something great about Britain, not just that we care about tackling global poverty or tackling climate change or helping those that don’t have what we have in this country.
BREAKING: Foreign aid backlash: Minister resigns after Boris announces cut
David Cameron is a former Prime Minister of the UK
"It was that we were actually going to do something about it and that we were going to lead and show the rest of the world.
"I saw as Prime Minister the effects of that leadership, what it brought for Britain as well as the amazing good it did putting food on people's tables, vaccinating children, stopping mothers from dying in childbirth.
"These were brilliant things we were doing and it said something brilliant about this country.
"I think it is sad that we are standing back from that."
He later added that he believed Rishi Sunak was "making a mistake" with the move.
Mr Cameron earlier said he "deeply regrets" the Chancellor's decision to reduce the overseas aid budget.
He tweeted: "0.7 percent is ultimately very simple. We share this planet with millions who are starving, with mothers who die needlessly in childbirth and with children who die of preventable diseases and with countries that are broken by conflict, corruption and poverty.
"The questions are: do we care, do we act and do we lead?
"The promise of 0.7 meant that we - Global Britain- answered 'yes' to all three.
"And that's a promise worth keeping."
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Rishi Sunak made the announcement in the House of Commons during his Spending Review on Wednesday
In another development a Foreign Office minister has resigned in protest against the Government's decision to cut the overseas aid budget, branding the move "fundamentally wrong".
Chancellor Sunak announced the aid budget will be cut to 0.5 percent of gross national income in 2021 – in spite of promises not to reduce it in the Conservative manifesto – adding the Government's "intention" is to return it to 0.7 percent when the fiscal situation allows.
Baroness Liz Sugg, whose brief included sustainable development, said pledges should be kept in the "tough times as well as the good".
In a letter to the Prime Minister, she wrote: "Many in our country face severe challenges as a result of the pandemic and I know the Government must make very difficult choices in response.
"But I believe it is fundamentally wrong to abandon our commitment to spend 0.7 percent of gross national income on development. This promise should be kept in the tough times as well as the good.
"Given the link between our development spend and the health of our economy, the economic downturn has already led to significant cuts this year and I do not believe we should reduce our support further at a time of unprecedented global crises."