The Italian, 60, takes over after the O's, 17th in League Two, ended Andy Hessenthaler's five-month reign as boss in late September.
He becomes Orient's eighth manager since Italian businessman Francesco Becchetti bought the club in 2014.
Interim boss Andy Edwards, who had overseen one defeat and one draw, reverts to his role as assistant boss.
Orient travel to Southend in the Checkatrade Trophy on Tuesday.
Leyton Orient have appointed former Sampdoria boss Alberto Cavasin as their new manager on a two-year deal.