Quintos will lead brand strategy, global communications, social media, corporate responsibility, global research, marketing talent development and agency management.
She will report to Dell chief executive and chairman, Michael Dell.
Her promotion comes after 10 years at the company, most recently as vice-president of marketing for Dell's global public business, covering higher education, government and healthcare institutional customers.
It also coincides with the end of the computer giant's three-year, full-service contract with WPP, which was negotiated by previous Dell global marketing head Casey Jones.
Last Friday (17 September), it emerged that Dell is reviewing its US business for consumer small, medium and public businesses from creative agency Y&R Brands and WPP shop Wunderman.
Dell has insisted that the review does not include the media assignment, currently held by WPP sister agency MediaCom, or the Dell branding business also held by Y&R Brands.
Michael Dell said: "Karen's success at Dell has come from her tremendous focus on our customers and her strong understanding of our commercial IT solutions.
"She is a world-class marketing professional and one of our most inspired and engaging leaders, and we are pleased to welcome her to our executive leadership team."