The Government has earmarked a £61.4 million warchest to fight the rising tide of plastic pollution in the world's oceans.
Theresa May announced the fund ahead of the Commonwealth Heads of Government meeting in London next week.
She is due to call on all of the 52 leaders present to sign up to the Commonwealth Clean Oceans Alliance - a strategy to help developing Commonwealth nations research and improve and waste management.
Four Commonwealth countries have already joined the UK in the alliance - New Zealand, Sri Lanka, Vanuatu and Ghana.
Downing Street said £25 million of the fund will be used to help researchers investigate the issue of marine plastic from a scientific, economic and social perspective.
A further £20 million will be used to curb plastic and other environmental pollution generated by manufacturing in developing countries and prevent it entering the oceans.
The remaining £16.4 million will be devoted to improving waste management at a national and a city level to stop plastics entering the water.
Following vocal public support for the issue, the Government pledged to match pound-for-pound public donations to tackle the issue of plastic waste via the UK Aid Match up to a total of £5 million.
The issue of plastic waste caused public outcry after Blue Planet II, narrated by Sir David Attenborough, highlighted the scale of the problem.
Speaking in advance of the summit, the Prime Minister said: "This week we will look closely at how we can tackle the many threats to the health of the world's oceans, including the scourge of marine plastic pollution.
"As one of the most significant environmental challenges facing the world today it is vital that we tackle this issue, so that future generations can enjoy a natural environment that is healthier than we currently find it.
"The UK public has shown passion and energy in the fight against plastic waste, and I believe the Commonwealth is uniquely placed to further this transformative action.
"It is a unique organisation with the strength and the commitment to make a difference."
She added: "If we stand together, we have the opportunity to send not only a powerful message to the world, but also to effect real change."
Britain, who is co-chairing the event with Vanuatu, will call on commonwealth nations to follow the UK's lead in banning microbeads and cutting down on single use plastic bags.
Following the announcement, WWF chief executive Tanya Steele said: "This alliance, and the leadership the UK government is showing through the Commonwealth, demonstrates that we're committed to being part of a global solution.
"Two billion people around the world lack access to effective waste collection, so much of the plastic they use ends up in our oceans.
"Devoting UK international development money to help poor communities clean up and better manage their waste isn't just good for nature, it's good for people too."