Subsequent monthly payments are also capped to £99 – with motorists paying 19.6p a mile on top for every mile they drive.
Fiat says that with the monthly payment and fuel factored in, the average 25-mile daily commute will cost £10.39.
According to research, those living in London pay, on average, £15.25 for their daily public transport commute.
To make the deal more tempting, Fiat is giving the first 500 miles for free.
“I am confident that one of the most affordable offers in Fiat’s history will become very popular with consumers over the coming months,” said Fiat UK country manager Francesco Vanni.
Fiat likens the deal to those found in the mobile phone sector – it comprises a low base rental price and any usage is calculated via the ‘pay as you go’ concept.
Mileage is tracked using an onboard black box, which monitors all vehicle movements.
So confident is Fiat in its new offer, the company has hinted there are already plans to extend it to other models within the Fiat, Abarth, Jeep and Alfa Romeo ranges.
The company has also separately launched a car finance package with job-loss protection.
How does the Fiat pay-as-you-go car lease work?
The Fiat 500 Mild Hybrid car lease is a four-year agreement – after which motorists hand back the car with nothing more to pay.
The upfront cost at the start of the lease is £99.
After that, the monthly cost for 47 months is again £99 – plus 19.2p for every mile driven.
This is all calculated though the onboard black box, so owners automatically pay the correct sum each month.
Fiat’s offer to give the first 500 miles free saves owners £96.
There is no upper mileage limit – owners can drive 20,000 miles a year if they wish (which would cost £3,840 a year).