Dr Sonja Niederacher

Sonja Niederacher is the Global Head of Restitution Research at Sotheby’s. She joined the company in 2024, bringing with her decades of expertise in Nazi-era provenance research in Europe and the United States. Her career spans academia, museums, and government institutions, giving her a uniquely multifaceted perspective and a deep understanding of the historical, ethical, and legal dimensions of restitution research.

At Sotheby’s, she acts as a trusted advisor to collectors and clients, guiding them through complex provenance as well as restitution matters related to sales and valuations. As a historian with a robust academic background, Dr Niederacher represents Sotheby’s before the scholarly community at international conferences and events. Internally, she leads the global research efforts of the Restitution Department. Her work on Gustav Klimt’s Portrait of Elisabeth Lederer along with two additional Klimt landscapes from the Leonard Lauder collection that sold for a record sum in New York in 2025, earned her widespread recognition.Collaborating closely with Sotheby’s Global Fine Art expert teams, she reviews the provenance of every artwork offered for sale, ensuring that full due diligence is applied. Her scholarly assessment of the merits of claims is pivotal to restitution processes mediated by Sotheby’s. She also provides internal training on World War II-era provenance issues, equipping art specialists and business experts with key knowledge.

Prior to joining Sotheby’s, she held senior provenance research positions at The Museum of Modern Art in New York and—appointed by the Austrian government—at the Leopold Museum in Vienna. In the latter role, she developed strong expertise in Austrian Modern Art, establishing herself as the worldwide leading provenance expert on the work of Egon Schiele and Gustav Klimt.