A strong Rodin influence is evident in his early work. His principal works include, “The Boy” (1885); “Cain” (1886), later destroyed; “Brotherly Love,” sometimes called “Two Friends” (1887); the allegorical “Two Natures” (1894, in the Metropolitan Museum, New York); “The Hewer” (1902, at Cairo, Illinois); “Great God Pan” Dodge Hall quadrangle, Columbia University campus, New York City; the “Rose Maiden”; the simple and graceful “Maidenhood”. In 1912 he completed several figures for the new state capitol at Harrisburg, Pennsylvania. A colossal statue of Abraham Lincoln, in 1917, was the subject of heated controversy because of its rough-hewn features and slouching stance. The first casting is in Cincinnati, Ohio (1917), the second in Manchester, England (1919), and the third in Louisville, Kentucky (1922).
The Great God Pan, one of the first works Barnard completed after his return to America, according to at least one account, was originally intended for the Dakota Apartments on Central Park West. Alfred Corning Clark, builder of the Dakota, had financed Barnard's early career; when Clark died in 1896, the Clark family presented Barnard's Two Natures to the Metropolitan Museum of Art in his memory, and the giant bronze Pan was presented to Columbia University, by Clark's son, Edward Severin Clark, 1907.
Interested in medieval art, Barnard gathered discarded fragments of medieval architecture from French villages. He established this collection in a churchlike brick building near his home in Washington Heights, New York City. The collection was purchased by John D. Rockefeller Jr. in 1925 and forms part of the nucleus of The Cloisters collection at the Metropolitan Museum of Art.
Barnard died following a heart attack on April 24, 1938 at the Harkness Pavilion, Columbia University Medical Center in New York. He was working on a statue of Abel, betrayed by his brother Cain, when he fell ill. He is interred at Harrisburg Cemetery in Harrisburg, Pennsylvania.