Over 20 countries, states and provinces have signed up to the Powering Past Coal Alliance at the COP23 United Nations climate change talks taking place in Bonn, Germany.
The group is aiming to completely phase out unabated coal "in a sustainable and ecomically inclusive way".
The inclusion of Canada and the UK, two of the United States' closest allies, sends a message that the rest of the world plans to continue on a path of emission reductions without the US.
The US president signaled his intention to remove the US from the 2015 Paris agreement unless it was able to renegotiate terms.
"All partners commit to supporting clean power through their policies... and investments, and to restricting financing for traditional coal power without carbon capture and storage," the statement from the 25 signatories said.
Announcing the UK was part of the new alliance, UK climate change minister Claire Perry said: "Reducing global coal consumption should be a vital and urgent priority for all countries and states. Unabated coal is the dirtiest, most polluting way of generating electricity.
"The Powering Past Coal Alliance will signal to the world that the time of coal has passed. The UK is committed to completely phasing out unabated coal-fire power generation no later than 2025 and we hope to inspire others to follow suit."
Coal supplied 9% of the UK's electricity in 2016, according to official data, down from 22% a year earlier.
Co-signatory Denmark aims to remove coal from its electricity supply by 2030. "The cost of renewable energy rattles down, and we have reached a point where new wind farms are cheaper than new coal power plants in Denmark," said Danish energy minister Lars Lilleholt.
"Therefore, the government says now that coal belongs to the past of the Danish electricity generation. We will send coal to retire by 2030. The future is associated renewable energy in Denmark.
State-owned energy firm Ørsted (formerly Dong Energy) earlier this year announced plans to ditch coal by 2023.
The coalition of 25 nations or sub-federal governments aims to have 50 members by the 2018 round of climate talks.
Partner countries, states and organisations confirmed as of 16 November, at 10am:
5. British Columbia
7. Costa Rica
14. Marshall Islands
17. New Zealand
23. United Kingdom