The car is known as the 500byDIESEL, and only 10,000 cars are being made available worldwide.
They are being sold through the , with users being given the chance to configure the car the way they want it, pay a deposit, track its production, and make a final payment and organise the best dealer from which to collect the vehicle.
The web-only sales strategy follows a venture by Fiat earlier this year, in which customers were offered the chance to pre-order one of 200 Abarth 500s by paying a deposit online, six months ahead of the official UK launch. The inventory sold out three months ahead of schedule.
Elena Bernardelli, marketing director for Fiat UK, said: "This new route to market is an exciting and futuristic development for Fiat. The Fiat 500 is also a perfect fit for Diesel and we are pleased to have this fantastic association with them."
Fiat's Style Centre in Turn worked with the Diesel design team to come up with the look of the car, which is billed as an 'urban survival vehicle'. It comes in a choice of metallic green, brown or black and features alloy wheels with the Diesel logo, Diesel side trim and yellow brake callipers.
The inside features denim upholstery and more Diesel logos.