Sachs was the chairman of the American Defense Harvard Group, which was created in 1940 to provide expertise on relevant cultural matters during the war. As a member of the Roberts Commission, he recruited many of his former students to serve in the MFAA – most prominently James Rorimer. His efforts unquestionably led to the protection, salvage, and restitution of countless works of art and other treasures.

The eldest son of prominent investment banker Samuel Sachs and Louisa Goldman Sachs, Paul attended Harvard University where he developed a passion for the arts and also began collecting prints and drawings with fellow classmate Edward W. Forbes. After graduating in 1900, he joined the family firm and became partner in 1904, but Sachs never abandoned his love for art. He became a member of the Visiting Committee for Harvard’s Fogg Art Museum in 1911. In 1914, his old friend, Edward Forbes, by then the director at the Fogg, persuaded Sachs to be assistant curator of the museum. Sachs left his business and joined the museum full-time in 1915. He was made an assistant professor in the department of fine arts at Harvard in 1917, associate director of the Fogg in 1923, and full professor in 1927. Together, Forbes and Sachs formed a team of fundraising, teaching and museum development which set a standard for academic museum direction.

In 1922, Sachs initiated his famous museum studies program – a groundbreaking course that was one of the first of its kind. His business experience helped teach art history students valuable, practical administrative skills. Another of his significant contributions to the discipline of art history was developing the dual skill of connoisseur-ship-scholarship in his museum students. Sachs provided his students with firsthand interaction with artworks, particularly his collection of prints and drawings, to hone their ability to discern quality and authenticity. His students went on to become prominent figures at prestigious institutions, most notably: Alfred H. Barr (Museum of Modern Art, New York), James Rorimer (MFAA officer and Director of the Metropolitan Museum of Art, New York) and Sydney J. Freedberg (Harvard Professor and Chief Curator at the National Gallery of Art, Washington). He retired from the Fogg Art Museum, along with his friend Forbes, in 1945, and left the art history department in 1948.

He died in Cambridge, MA in 1965.