The pledge was made as the World Mayors Summit started in Buenos Aires, Argentina, with C40 Chair and Mayor of London Sadiq Khan expected to unveil his manifesto later today.
C40 mayors represent hundreds of millions of citizens and a quarter of the global economy.
C40 research shows that 50 million green jobs are needed for C40 cities to deliver their fair share of halving emissions in line with the Paris Agreement.
It is estimated that comprehensive climate action by C40 cities would result in a third more jobs compared to today’s “business-as-usual” economic approach.
The authors of the report also predict that air pollution could be reduced by up to a third and deliver $280 billion (£250bn) economic benefits in C40 cities.
Sadiq Khan, Mayor of London and Chair of C40 Cities, said: “Investing in the jobs and skills of the future will help us to tackle inequality as we tackle the climate crisis.
“I am so proud to stand united in action with my fellow C40 city Mayors to drive the creation of 50 million good, green jobs by the end of this decade.
“London will lead by example as we double the size of our green economy and establish good, green jobs accessible within communities that need them most.
“There is no time to waste. The best time to act on good, green jobs was yesterday; the next best time is today.”