[8][9] Development of the vehicle by PSA Group took seven years due to its radical concept, and was led by project manager Aurélie Bresson.

[12] Its design concept was also featured by the Citroën C5 X, which shares the same platform (long-wheelbase EMP2 V3[13]) and height with the 408.

Due to its body shape, the 408 achieves a low coefficient of drag of 0.28, on par with traditional saloons.

[12] The 408 also shared the same headlights, taillights, and dashboard design as the third-generation 308, which was developed alongside it.

The petrol engine will be replaced with a mild hybrid unit in late 2023 and a battery electric model called the e-408 will follow.