William Adair is recognized for his work as a conservator and historian of picture frames. In the early 1970s, he began working at the Smithsonian's National Portrait Gallery, where he became a museum specialist focusing on gilding, frame history, and the connections between fine art and traditional decorative arts. He founded Gold Leaf Studios in 1982 in Washington, DC, where he built his renowned career as a frame maker and gilder. Adair leads workshops, lectures, and organizes exhibitions about frame history, frame making, and gilding.

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Adair's artwork is in numerous collections, including the Smithsonian American Art Museum. In 1991, he received the Rome Prize in design from the American Academy in Rome. In 2011, Montgomery College hosted a retrospective exhibition of his career as an artist and frame maker.

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He is represented by Govinda Gallery in Washington, DC.