He joined Lazard Freres in 1908 and served in France as an Army captain during World War I. In 1916, his father retired as partner at Lazard and Altschul took his place in the firm as one of five partners. In the 1920s, he was awarded the Legion of Honor by the government of France after giving successful advice on how to stabilize the French franc. In the 1930s, he was part of the committee that governs the New York Stock Exchange before moving on to work with the Chase National Bank. In 1934, he established Overbrook Press which specialized in illustrated, limited edition books for collectors. In 1943, Altschul began working with Lazard Freres as a senior partner. Later he moved on again to General American Investors Company, and maintained his position as an executive until his retirement in 1961.
