Isidor Straus was born into a Jewish family in Otterberg in the former Palatinate, then ruled by the Kingdom of Bavaria. He was the first of five children of Lazarus Straus (1809–1898) and his second wife Sara (1823–1876). His siblings were Hermine (1846–1922), Nathan (1848–1931), Jakob Otto (1849–1851) and Oscar Solomon Straus (1850–1925). In 1854 he and his family immigrated to the United States, following his father Lazarus, who immigrated two years before. They settled in New York City, where Lazarus had convinced Rowland Hussey Macy to allow L. Straus & Sons to open a crockery department in the basement of his store. Isidor Straus worked at L. Straus & Sons, which became the glass and china department at Macy’s. In 1888, he and Nathan Straus became partners of Macy’s. By 1896, Isidor and his brother Nathan had gained full ownership of R. H. Macy & Co. In 1871, Isidor Straus married Rosalie Ida Blun (1849–1912).  Isidor and Ida were a devoted couple, writing to each other every day when they were apart. He served as a U.S. Congressman from January 30, 1894, to March 3, 1895, as a Democratic representative to New York’s 15th congressional district. Also, Straus was president of The Educational Alliance and a prominent worker in charitable and educational movements, very much interested in civil service reform and the general extension of education. He declined the office of Postmaster General which was offered him by U.S. President Grover Cleveland.

Traveling back from a winter in Europe, mostly spent at Cape Martin in southern France, Isidor and his wife were passengers on the RMS Titanic when, on the night of April 14, 1912, it hit an iceberg. Once it was clear Titanic was sinking, Ida refused to leave Isidor and would not get into a lifeboat without him. Although Isidor was offered a seat in a lifeboat to accompany Ida, he refused seating while there were still women and children aboard and refused to be made an exception. According to friend and Titanic survivor Colonel Archibald Gracie IV, upon seeing that Ida was refusing to leave her husband, he offered to ask a deck officer if Isidor and Ida could both enter a lifeboat together. Isidor was reported to have told Colonel Gracie in a firm tone: “I will not go before the other men”. Ida insisted her newly hired English maid, Ellen Bird, get into lifeboat #8. She gave Ellen her fur coat, stating she would not be needing it. Ida is reported to have said, “I will not be separated from my husband. As we have lived, so will we die, together.” Isidor and Ida were last seen on deck arm in arm. Eyewitnesses described the scene as a “most remarkable exhibition of love and devotion.” Both died on April 15 when the ship sank at 2:20 am. Isidor Straus’s body was recovered by the cable ship Mackay-Bennett and brought to Halifax, Nova Scotia, where it was identified before being shipped to New York. He was first buried in the Straus-Kohns Mausoleum at Beth-El Cemetery in Brooklyn. His body was moved to the Straus Mausoleum in Woodlawn Cemetery in the Bronx in 1928. Ida’s body was never found. Isidor and Ida are memorialized on a cenotaph outside the mausoleum with a quote from the Song of Solomon (8:7): “Many waters cannot quench love—neither can the floods drown it.”