The Microsoft founder urged the UK to keep spending at least 0.7% of national income - saying it's about goodwill and humanity. He added that reducing the spending would cost lives around the world.
Simon Kirkland, Christian Aid's Acting Senior UK Political Adviser, told Premier News Hour his statement comes in good timing.
He said: "The U.N. has recently said that round 20 million people are facing famine conditions in places like South Sudan, Yemen, Nigeria and other places.
"We have real humanitarian need around the world now".
Gates' statement came after Theresa May refused to say whether the £12 billion commitment would be included in the Conservative party's election manifesto on Wednesday.
Kirkland told Premier the Prime Minister has supported the 0.7% commitment in the past, but staying tight lipped about the topic is a little worrying.
He said: "We urge her and all political parties to make that commitment now so that we can move into this election with the cross party commitment on aid secure".
Kirkland adds that the British government should do its part in persuading other countries to make the 0.7% foreign aid commitment.
When asked for a response about people that say the UK is already spending too much helping other countries, Kirkland said it is not only a moral responsibility and a practical one.
He said: "The average UK tax payer pays less than £1 a week to fund the 0.7% commitment.
"It's helping save lives around the world and we're making real progress.
"For example, extreme poverty has halved in the last 40 years and we're seeking to cut it out completely by 2030.
"While I recognise there are needs in the UK, I think there are also needs around the word."