The 35-year-old former international stand-off becomes the first French coach of the Perpignan-based club.
Frayssinous replaces Trent Robinson, who has left France for a post at Sydney Roosters in Australia.
Frayssinous is five months the junior of the previous youngest Super League coach, Bradford's Francis Cummins.
Frayssinous had been part of the Dragons' coaching staff and played for them when they made their Super League bow with a 38-30 win against Wigan in 2006.
The former assistant coach of the France national team has signed a two-year deal, with the option of a third season.
Laurent Frayssinous has been appointed the head coach of Catalan Dragons on a two-year contract, and becomes the youngest team boss in Super League.