"He not only brings to Microsoft a strong breadth of online experience but also dedicated leadership and business acumen," she added.
Mr Fiorentini spent the last 11 years with Yahoo! in Australia and South America, most recently as chief operations officer for Yahoo!7.
Somewhat presciently, he said "I'm thrilled to join Microsoft Australia when strong consumer brands such as Windows Phone 7 are being brought to market."
Mr Fiorentini added "My new role will concentrate on customer satisfaction, product share, revenue and growth of our consumer and online division. My team is absolutely committed to telling the story of how we connect consumers with what they want, value and love using Microsoft software."
His predecessor, Alex Stewart, has been appointed CFO of ninemsn.