Askou led Motherwell to fourth place in the Scottish league and now joins Toulouse on a contract whose duration was not disclosed.
This former central defender previously coached in Denmark and the Faroe Islands, where he achieved a league and cup double with HB Torshavn in 2020.
He was also an assistant at Czech side Sparta Prague and Danish club FC Copenhagen, as well as head coach of IFK Göteborg in Sweden.
Toulouse finished 10th in the French Ligue 1 2025-2026, which ended last weekend.