Lamouchi, 54, replaces Sami Trabelsi, who was sacked after Tunisia's defeat to Mali in the Africa Cup of Nations last 16 earlier this month.
Lamouchi, who coached the Ivory Coast at the 2014 World Cup, has signed a contract until 2028, the federation announced.
Born in France of Tunisian heritage, he played as a midfielder for Monaco, Inter Milan and Marseille.
Aside from the Ivory Coast, he has coaching experience at club level with Rennes, Nottingham Forest, and Cardiff City, helping the side avoid relegation from England's second-tier Championship in 2022/23.