Born to a Jewish family, the son of Jacob Wertheim of Hartford, Connecticut, and his wife, Hannah Frank of Hoboken, New Jersey, Wertheim was educated at the Sachs School in New York. He then graduated from Harvard University in 1906 with a B.A. and received his M.A. in 1907. In his freshman year, he lived in Matthews Hall in Harvard Yard. He began work at his father's firm, the United Cigar Manufacturers Company. He would later inherit nearly half a million dollars from his father, due to his success with the company. In 1915, he entered into a career as an investment banker in New York, and four years later would become a firm partner of Hallgarten & Company. He founded his own firm Wertheim & Company in 1927, developing a very successful business in mergers and acquisitions, and becoming wealthy in the process. During World War II, he served as a dollar-a-year man on the War Production Board in the administration of President Franklin D. Roosevelt.