Neiman Marcus Group Ltd., the luxury retailer saddled with debt from two leveraged buyouts, is preparing to appoint a new chief executive, according to people familiar with the situation.

Karen Katz, a Neiman lifer who has served as CEO and president since 2010, is stepping aside and will be succeeded by former Ralph Lauren Corp. executive Geoffroy van Raemdonck, the people said. Ms. Katz, 60 years old, plans to retire from her executive duties but would retain her board seat, the people said.

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