Australia, Fiji, Kenya and St Lucia have now formally joined the Commonwealth Clean Oceans Alliance [CCOA].
The coalition, led by the UK and Vanuatu is already supported by New Zealand, Sri Lanka and Ghana.
Environment Minister Thérèse Coffey anounced the development at a meeting of over 30 Commonwealth countries in London on Tuesday.
The Alliance, which aims to bring together Commonwealth Countries against the growing problem of plastic pollution threatening the worlds oceans, was first announced by the UK Prime Minister Theresa May during a meeting of the Commonwealth Heads of Government Meeting which took place 16-18 April this year.
Each country in the Alliance is expected to take steps reduce plastic waste.
Thérèse Coffey said: “Marine plastics pollution is one of the greatest environmental challenges facing the world today, requiring a truly global approach to developing a solution.
“By joining together the expertise and ambitions of the Commonwealth countries, we can make huge strides towards eliminating all single use plastic from our oceans.
“I thoroughly enjoyed hearing from other countries on how they are approaching this challenge, and look forward to seeing what difference we can make together.”
Prime Minister Theresa May has already commited a £61.4 million package of funding, the Commonwealth Oceans Plastic Package, of which £25million is allocated towards researching the scientific, technical, economic and social perspective of plastic waste pollution.
Details were also announced at the meeting about the Global Plastics Action Partnership, an initiative to tackle global plastic pollution in rivers, deltas and oceans, which is linked to the CCOA and funded by Defra. Plasic pollution hotspots ln Southeast Asia, West Africa and a Small Island Developing State will be targeted in three initial projects.