The Italian chef, who left L'Anima in March, will re-open D&D's Savile Row restaurant later this year following an extensive refurbishment.
He said: "It is a joy for me to join a company for whom I have such respect for their quality of chefs and food. I believe now is the right time for me to move into the West End and I am thoroughly looking forward to making Sartoria one of London's best Italian restaurants."
D&D managing director David Loewi said: "We are absolutely delighted and thrilled that Francesco will be heading up the new Sartoria. He is undoubtedly one of the most gifted Italian chefs cooking in London today and will bring something very special to D&D London".
Calabrian-born Mazzei, who helped launch L'Anima in 2008, left the City of London restaurant in March for reasons still unknown. A statement from the restaurant said he had been replaced by head chef and long-standing right-hand man Antonio Favuzzi.