The initiative aims to shed light on how climate change is having an impact across the world and place pressure on governments to take action.
People can contibute their views by using the hashtag #TakeYourSeat. A selection of comments will be shaped into an speech that Attenborough will deliver to world leaders at the climate change summit COP24 in Poland next month.
"We all know climate change is a global problem, and that it requires a global solution," Attenborough said.
"This is an opportunity for people from across the globe, regardless of their nationality or circumstances, to be part of most important discussion of this century: the unprecedented action needed to reach the Paris Agreement targets.
"I encourage everyone to take their seat and to add their voice so that the People’s Seat Address truly represents a mix of voices from across the world."
WPP agencies Burson Cohn & Wolfe, Finsbury, Grey, Kantar TNS & Lightspeed, MediaCom, The Social Partners and Town Productions have worked in partnership with various UN agencies to bring the campaign to life.
These include the UN Department of Public Information, the United Nations Office at Geneva, the United Nations Framework Convention on Climate Change. Facebook, Circle AI, Whalar, ITB and Getty Images are also supporting the campaign.
Michael Møller, the director-general of the United Nations Office at Geneva, first put forward the initiative. He said that climate change was becoming so severe that only collective global action could tackle the problem.
"If we don’t, we all fail with catastrophic consequences," Møller said. "The People's Seat initiative provides the impulse for seriously ramping up global solidarity, especially among the young who, at the end of the day, are the ones who will have to deal with the mess we have left them with."
UN under-secretary-general for global communications Alison Smale said the initiative is calls on citizens to take action in ways that are "feasible, fresh and have an impact".
"People need to be empowered in their own lives to be the change that we need for a sustainable world," Smale added. "We welcome the use of cutting-edge technology to help everyone around the world reduce emissions through the Actnow.bot."
The COP24 climate change summit takes place in Katowice, Poland, from 2-14 December.