After receiving a Mellon Fellowship he began studying at The Metropolitan Museum of Art, where he was appointed in 1980 as curator and would spend the rest of his career.
He organized numerous exhibitions, wrote seven books, including several on Rembrandt and Vermeer, and produced catalogues of the Museum's Dutch and Flemish paintings.
The 2001 Liedtke-curated show, "Vermeer and the Delft School" was said to be the most popular art exhibition that year, attracting 555,000 visitors during its three-month run.
[10] Most recently, he worked on "El Greco in New York," a collaborative project that was co-curated with Keith Christiansen,[11] with the Hispanic Society of America and the Frick Collection held at the Metropolitan Museum of Art from November 4, 2014 to February 1, 2015.
[2][15] Thomas Campbell, director of the Metropolitan Museum of Art, described him as "one of the most distinguished scholars of Dutch and Flemish painting in the world.