The app for iPhone will be followed by a version for Android smartphones.
It includes maps to 23 UK airports and supplies a voucher to phones to show at airport car park gates.
Booking on the app qualifies users for up to 60% pre-booking discount, even if travellers are on the way to the airport, the company claims.
To mark the launch, Park & Go is giving away an iPod touch in a competition on its Facebook page.
Park and Go managing director David Howard said: “Busy people frequently forget to book airport parking. We get drivers on the M25 phoning at the last minute saying they have forgotten to book.
“The drive-on rate is more costly than the pre-booked rate, so if they have our new Park and Go app on their iPhone, they can even book on the way to the airport – and still be classified as a pre-booked client to get the discount.”