John Prescott is returning to front-line politics as a special adviser to Ed Miliband with responsibility for climate change.
The former deputy PM will focus on trying to help a future Labour government seek agreement at climate change talks due to take place in Paris in December, Labour sources say.
Mr Miliband thought there was "no-one better" for "bashing heads together", a source said.
Lord Prescott left the Commons in 2010.
Lord Prescott, who turns 77 in May, served for 13 years as deputy leader of the Labour Party under Tony Blair. He resigned as deputy prime minister in 2007.
His time in government was marked by controversy over a two-year affair with a secretary and an incident when he punched a man who threw an egg at him during a general election campaign.
In 2012 he stood as the Labour candidate in the election to be the first police and crime commissioner for Humberside Police, but lost to Conservative Matthew Grove.
The BBC's political correspondent Robin Brant said the appointment may be seen as an attempt by Mr Miliband to deal with a threat from UKIP, who are trying to target traditional Labour voters in the north of England.
A renewed focus on climate change issues is also likely to be seen as an attempt to rebut advances from the Green Party as the election gets closer, our correspondent added.
Talk about desperate!
