The British government of Theresa May committed 88 million US dollars to the Commonwealth Clean Oceans Alliance.
The funding package is billed at helping to boost global research and assist Commonwealth countries stop plastic waste from entering the oceans in the first place.
Speaking ahead of the Commonwealth Heads of Government meeting in London next week, Ms May announced that New Zealand, Ghana and Sri Lanka had joined the Alliance.
Together with Vanuatu as joint chair, Britain called on other countries to pledge action on plastics.
This can include a ban on microbeads, cutting down on single-use plastic bags, or other steps to eliminate avoidable plastic waste.
Developing countries who sign up to the Alliance are eligible to bid for partnership support to improve waste management systems and implement other initiatives to reduce the plastic waste reaching oceans.