Gordon Brown is among more than 130 political figures, celebrities, entrepreneurs and investors who have called for "long-view leadership" in the face of rising threats to humanity.
They have signed an open letter from The Elders and the Future of Life Institute to underscore the importance of tackling risks such as the climate and nature crisis, pandemics, nuclear weapons and ungoverned artificial intelligence (AI).
The letter, published on Thursday, says world leaders are failing to act or co-operate over the threats as millions of lives and livelihoods already face catastrophic consequences.
"Long-view leadership" is defined by the signatories as the "determination to resolve intractable problems not just manage them, the wisdom to make decisions based on scientific evidence and reason, and the humility to listen to all those affected".
Signatories include former Irish president Mary Robinson, former UN secretary general Ban Ki-moon, former Colombian president Juan Manuel Santos and former executive secretary of the United Nations Framework Convention on Climate Change, Christiana Figueres.
Businessman Sir Richard Branson, singer Annie Lennox, former Unilever chief executive Paul Polman and J. Robert Oppenheimer's grandson, Charles Oppenheimer, have also signed.
The letter comes in the run-up to the Munich Security Conference, at which government officials, military leaders and diplomats will meet to discuss international security.
The signatories urged those at the conference to address these challenges head-on as preparations continue for September's UN Summit for the Future.
They also invited members of the public across communities, generations and political spectrums to sign the letter.
The Elders and the Future of Life Institute have stressed the need for urgent multilateral action, outlining measures such as financing the transition away from fossil fuels, concluding an equitable pandemic treaty, restarting nuclear arms talks and building global governance for AI.
Ms Robinson, chairwoman of The Elders, a group of global leaders founded by the late former president of South Africa, Nelson Mandela, said: "Our world is in grave danger, but with long-view leadership rooted in truth, justice and inclusion, we can still step back from the precipice.
"This does not mean global decision-makers should neglect the challenges we face today; it means making decisions that go beyond short-term politics and delivering solutions for people struggling now, as well as future generations."
Mr Ban, who is also deputy chairman of The Elders, said: "The range of signatories to this open letter makes clear our shared concern: we need world leaders who understand the existential threats we face and the urgent need to address them.
"This can only be done through decisive co-operation between nations.
"We need to revitalise multilateralism for the sake of our common future. This means upholding the international rule of law and being open and accountable for the decisions we must take."
Mr Santos said: "Too many leaders in politics and business today are following short-term agendas.
"They need to look beyond electoral and reporting cycles and instead pursue policies based on solidarity and sustainability.
"The need for principled and effective leadership has never been greater. Only a multilateral approach towards the goal of net zero, with renewed pressure on big emitters, will help avert catastrophe."
