In 1886, Carstairs began working for his father-in-law 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." In 1928, upon Roland Knoedler's retirement, Charles Carstairs, his son Carroll Carstairs, Charles Henschel, and Carmen Mesmore took up the management of the Knoedler & Co. From this point, Charles Carstairs acted as chairman of the board at Knoedler & Co.
Carstairs acted as Frick's preferred dealer for some time. The large quantity of Old Master Paintings in Frick's collection demonstrates Carstairs' influence on Frick's taste. In 1908, Frick wrote in a letter to Carstairs "there is no-one whose judgment of the beautiful I have more confidence in than yours". In his relocation from Pittsburgh to New York, Frick was thrown into an increasingly competitive environment of conspicuous consumption. Carstairs turned Frick's attention to increasingly expensive Old Masters paintings as well as artworks that carried social prestige, such as aristocratic portraits, and encouraged Frick to invest in such art as a means of bolstering his reputation. The two remained close friends over Frick's lifetime. Not only did Carstairs aid in the construction of Frick's East 70th Street mansion but he also acted as an honorary pallbearer at Frick's funeral.
Personal life
In 1886, Carstairs married Esther Holmes Haseltine. Carstairs and Haseltine had four children, Charles Haseltine Carstairs, Carroll Chevalier Carstairs, James Stewart Carstairs and Elizabeth “Lily” Haseltine Carstairs. In 1903 Carstairs met the American actress, Elizabeth Stebbins, while crossing the Atlantic, he on a buying trip for Knoedler Gallery, and she to perform on the London stage. A romance ensued, and Carstairs divorced his wife, Esther, later that year. He married Elizabeth Stebbins in 1905 and settled in the fashionable Mayfair district of London. In 1928, shortly after being announced chairman of the board for Knoedler & Co., Charles Carstairs died of a heart attack.
