Both the Golf and Octavia will come with a 217bhp 2.0-litre petrol engine, although the Golf GTI will also have a Performance version that boosts power to 227bhp.
The Leon will get the same limited-slip differential as the Golf GTI Performance Pack, but despite this and the extra power, the Leon will not come with styling to match.
'It will look more understated than previous Cupras not so boy racer-ish,' said Fermin Soneira Santo, Seat's director of vehicle and chassis development.
The Leon will come in three- and five-door versions, while a more practical estate version, or ST, is likely to arrive later.
Pricing will be revealed closer to the Leon Cupra's launch, which is expected to be late this year or early 2014. However, Santo said that prices will be competitive with the Golf GTI.
'We know the Golf GTI has a strong image, so we know the Cupra can't be too much more expensive,' he said.