David Cameron says that developing family planning strategies is "fundamental" to tackling global poverty.
The Prime Minister made his comments as the Government pledged to donate more than £1 billion to help family planning services in the developing world.
In a bid to help 24 million girls and women in the world's poorest countries, British aid will be doubled for eight years.
Cash donated to family planning services will increase from £90 million each year to £180 million - more than £1.4 billion in total.
Speaking to health leaders from around the world at the London Family Planning Summit, Mr Cameron said: "Women should be able to decide freely and for themselves whether, when and how many children they have.
"It is absolutely fundamental to any hope to tackling poverty in our world. Why? Because a country cannot develop properly when its young women are dying from unintended pregnancy and when its children are dying in infancy.
"In a way it is so simple. Healthy empowered women mean healthy strong families mean healthy strong children mean healthy strong countries. It is as simple and straightforward as that."
The summit, which is hosted by the Government and the Bill and Melinda Gates Foundation, also aims to encourage poor countries to develop their policies to support the rights of women.
Various governments and charitable organisations donated more than 4.6 billion US dollars (£2.96 billion) towards developing family planning services by 2020, International Development Secretary Andrew Mitchell said.
Mr Mitchell said: "There has been a huge amount of support which will allow us to say that today has been a success. What we are trying to do here is to halve the number of women in the poor world who want to have access to contraception but do not have it. It will take us eight years to achieve that but if we are able to follow through with the commitments and the pledges that have been made today that should enable us to reduce that number by half."