Carleton, "Carly", Fiorina, recently named the most powerful woman in American business by Fortune magazine, becomes one of only three women heading Fortune 500 companies by taking over from Lew Platt as president and chief executive of the $47bn-turnover company. The others are Jill Barad of the toymaker Mattel and Narion Sandler of Golden West Financial Corp.
Ms Fiorina, who was president of the fastest-growing division of Lucent Technologies, the telecommunications equipment firm spun out of AT&T in 1996, is the first HP chief executive appointed from outside in the company's 60-year history.
The choice of Ms Fiorina over five other candidates is the culmination of a search that began earlier this year when Mr Platt announced he was splitting the company into two and stepping down. He will remain as chairman until his retirement at the end of the year.
Ms Fiorina, a philosophy and history graduate who moved into business after dropping out of law school and a short spell as a teacher, will run the larger company selling computers and printers. A smaller firm, as yet unnamed, will concentrate on measuring equipment, and will be run by HP veteran Edward Barnholt.
The appointment was greeted enthusiastically by the market and by commentators. HP shares hit a record $117.5 and JP Morgan analyst Greg Geiling rated the decision "an absolutely phenomenal hire".