ARMONK, N.Y. — Virginia Rometty, IBM Corp.’s president and CEO, is taking on the added role of chairwoman next week, as Samuel Palmisano prepares to retire at the end of this year.

The company said Tuesday that Rometty, 55, will take on the expanded role on Oct. 1. Palmisano, 61, will serve as a senior adviser until he retires in December.

Rometty, the company’s former sales and marketing chief, became IBM’s ninth CEO and its first female chief executive officer in January.

After joining the company in 1981 as an engineer, Rometty later was instrumental in the formation of IBM’s business services division, including overseeing the $3.5 billion purchase of PricewaterhouseCoopers’ consulting business in 2002, which was a key element of a strategy that has made IBM a heavily copied company.

She is “more than a superb operational executive,” Palmisano said when she was promoted to CEO.

IBM has sustained a nearly decade-long streak of earnings growth as it shook off the economic jitters that have undercut several other technology companies.

Rometty was in the Lowcountry in April when IBM held its annual meeting of shareholders at the Charleston Area Convention Center in North Charleston.

Her election to board chairman was announced after U.S. stock markets closed Tuesday. Shares of IBM closed down 31 cents to $204.98.