Since leaving the Obama Administration and ostensibly retiring, Kerry has signed an agreement to publish his memoirs and commentated on American politics.
The former presidential nominee in 2004 has been a fierce critic of Donald Trump's presidency and was on a policy group for Biden on climate change after the primary election season.
Asked about Biden's suitability for the presidency in December 2019, Kerry said: "He'll be ready on day one to put back together the country and the world that Trump has broken apart."
As special envoy, Kerry would be responsible for attending events designed to reach consensus on climate issues, including COP26, which is being hosted in Glasgow next year.
British Prime Minister Boris Johnson has invited Biden to attend COP26 himself.
In a call to the President-elect yesterday, Johnson congratulated Biden and suggested the UK and US could work together on climate policy.
A statement released by Downing Street said the leaders share priorities on "tackling climate change, promoting democracy, and building back better from the pandemic".
Biden has pledged to rejoin the Paris accords, an international agreement on climate and emissions Trump abandoned.
The Paris accords were originally signed by Kerry on behalf of the US.
Biden has also vowed to make US electricity production carbon-free by 2035 and to achieve net-zero emissions by 2050. The UN Climate Change Conference was delayed by the pandemic.