Charles Carstairs (August 1865 - July 1928) was an American art dealer. Throughout his career, Carstairs encouraged American clients to invest in European Old Master paintings. He worked closely with industrial magnate Henry Clay Frick, and was responsible for Frick's acquisition of the 'Ilchester Rembrandt' in 1906. Carstairs also worked with Joseph Widener, an American art collector and founding benefactor of National Gallery of Art in Washington, D.C.
Carstairs was born in Philadelphia on August 2, 1865, the 3rd son of James Carstairs and Mary White Carstairs (née Haddock).
In 1886, Carstairs began working for his father-in-law (Charles Field Haseltine) at Haseltine Gallery, at 1125 & 1127 Chestnut Street in Philadelphia. After working for Haseltine for eight years, Carstairs began working for Knoedler & Co. in New York City. In 1897, Carstairs was sent to Pittsburgh to lead the newly opened Knoedler & Co. branch at 432 Wood Street. Here, he began promoting Old Master paintings to Pittsburgh's industrial rich. From Pittsburgh, Carstairs moved to England in 1908 to lead Knoedler's London branch, which had opened in 1902 at 15 Old Bond Street. Carstairs reoriented the London gallery's focus from contemporary Parisian artists to Old Master paintings. The outbreak of World War I interrupted international trade, but also lead to the movement of many Old Master Art works to the United States. This movement of art works was advantageous, both to American dealers such as Knoedler & Co. and collectors such as Henry Clay Frick. In 1915, Carstairs stated, "England acquired her great Masterpieces during the French Revolution and Napoleonic Wars and now America's opportunity has come."