Matt Damon and Malala Yousafzai among supporters of Action/2015 campaign to ensure success at UN summits on development goals and climate change

Celebrities and campaigners including Matt Damon, Bill Gates, Jody Williams and Malala Yousafzai are joining forces to launch an international campaign to persuade the planet’s leaders to make 2015 the defining year in the fight against world poverty and climate change.

The campaign action/2015 – which launches on Thursday backed by more than 1,000 organisations across 50 countries – is focused on securing successful outcomes for two pivotal UN summits, one in September on remodelled development goals, and the other in December in Paris on a new international agreement on climate change.

In Britain, the campaign’s specific aim is to ensure politicians do not put the issues on the backburner during a general election that will inevitably be dominated by domestic issues.

In a letter to David Cameron, the celebrities, businessmen and Nobel peace prize winners tell the prime minister that the summits represent “the opportunities of a lifetime, yet with months to go few leaders are playing the leadership roles we need”.

They add: “If this does not change, we fear you and your fellow leaders could be sleepwalking the world towards one of the greatest failures of recent times.”

Other signatories include Bono, Desmond Tutu, Richard Branson, the entrepreneur Mo Ibrahim, the actor Aamir Khan, the Avaaz network founder Ricken Patel and Queen Rania of Jordan.

Cameron, who flew to the US on Wednesday, met some of the campaigners before he left. And in a speech on Thursday, Ed Miliband will endorse the campaign. The Labour leader will say: “I know tackling climate change, global poverty and inequality are not as fashionable as they once were. But I also know they are more important than ever.

“For me, they are not luxury items in our programme for change. They are not part of a branding exercise. They go to the heart of my beliefs and the reason why I entered politics.”

Nick Clegg, the Liberal Democrat leader, also acknowledged the campaign’s importance, saying: “Whatever the colour of the next government, I want the UK to seize 2015 as a crucial opportunity to take big global decisions.”

The campaign’s vast international scale has meant the aim at the outset is as much raising awareness of the importance of the summits as pushing specific demands.

The goals include:

• An end to poverty in all its forms, including UK backing for zero-based targets in strategic development goals such as poverty and child mortality.

• Meeting fundamental rights and tackling inequality and discrimination, and for this to be a priority for the UN framework agreement.

• An accelerated transition to 100% renewable energy, requiring UK commitment to this as the long-term goal for UN climate change negotiators.

Speaking for action/2015, Ben Jackson of Bond, the umbrella body for UK non-governmental organisations, said: “If we get this wrong, we could see the number of people living in poverty increase for the first time in our generation. But if we get it right – tackle poverty, inequality and climate change – we could eradicate extreme poverty within a generation.

“The UK has the potential to play a critical galvanising role on these issues, but we’re worried, with a UK election in the middle of the year, they might take their eye off the ball.”

According to new research, almost a billion extra people face a life of extreme poverty if the two summits fail to agree ambitious goals backed by financing packages.

The data, released by the action/2015 coalition, shows that the number of people living in extreme poverty – defined as less than $1.25 (80p) a day – could be reduced dramatically from more than 1 billion to 360 million by 2030.

Based on work by the University of Denver, in the year 2030, about 4% of the global population would live in extreme poverty, compared with 17% today, if critical policy choices on inequality, poverty investment and climate change are made this year and implemented thereafter. Under the best case scenario the number of people living in poverty could be reduced to 360 million by 2030. In the worst case scenario the number of people living in poverty could increase to 1.2 billion, a difference of 886 million.