Appointment arrives after Nancy Daniels, who previously held the exec veep post, was upped to general manager of TLC.
She has been with the Discovery Communications family since 2008.
"Denise is a perfect fit for this position," said O'Neill. "Having worked on both Discovery and TLC, she's a television executive who gets what both men and women of all ages want to see. Her track record of bringing quality programming to the Discovery family speaks for itself. I've worked with Denise for over six years now and I'm thrilled to grow this relationship and keep it going strong."
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