He helped finance the expansion of American railroads and the Japanese military efforts against Tsarist Russia in the Russo-Japanese War.

[2][3] He also became a director of many important corporations, including the National City Bank of New York, Equitable Life Assurance Society, Wells Fargo & Company, and the Union Pacific Railroad.

One ancestor, David Tevele Schiff, became lead rabbi in Great Britain and from 1765 until his death was acting head of the London Synagogue.

[4][5] After the American Civil War had ended in April 1865, Schiff came to the United States, arriving in New York City on August 6.

Along with H. B. Claflin, Marcellus Hartley, Robert L. Cutting, and Joseph Seligman, he was a founder of the Continental Bank of New York in August 1870.

[6] Schiff accepted Kuhn's invitation in January 1875, bringing to Kuhn, Loeb & Company his connections with Sir Ernest Cassel of London, Robert Fleming of Dundee (later of London), and Edouard Noetzlin [fr] of the Banque de Paris et des Pays-Bas (Bank of Paris and the Netherlands or Paribas).

He was elected a director of Wells Fargo & Company in September 1914 to succeed his brother-in-law, Paul Warburg, who had resigned to accept appointment to the original Federal Reserve Board.

It is quite likely Schiff also saw this loan as a means of answering, on behalf of the Jewish people for the antisemitic actions of the Russian Empire, specifically the recent Kishinev pogrom in 1903.

Since their domestic economy was still developing, Japan's military was dependent on massive imports of munitions, purchases made possible by Schiff's loan.

[citation needed] Schiff forbade any of the funds from his loans from going to the Russian Empire, due to the Tsarist regime's oppression of the Jewish people.

In addition to repeated public statements of support, he used both his personal wealth and the resources of Kuhn Loeb to float large loans to Kerensky's regime.

He founded the Jewish Industrial Removal Office which relocated New York immigrant Jews to the Western United States.

[20] On his 70th birthday, he distributed $700,000 among various charitable organizations and public institutions[21] Schiff believed in the Talmudic principle that "twice blessed is he who gives in secret."

He did not permit his name to be attached to the buildings he sponsored, with the one exception of the Schiff Pavilion at his Montefiore Hospital, and never discussed the size of his gifts.

[16] The Action Française movement and its leader, Charles Maurras, claimed that Schiff was thoroughly pro-German and had worked to prevent American entry into World War I. Maurras went so far as to suggest that a telegram from Schiff and other prominent American Jewish leaders convinced President Wilson to give in to certain German arguments at the post-war peace negotiations, including allowing Upper Silesia to have a plebiscite rather than being ceded to Poland.

Despite not agreeing fully with the ideas of Theodor Herzl, and in fact believing that Zionism would cause Americans to question his loyalty, he donated to many Jewish projects in Israel, including the Technical Institute of Haifa.

Journalist George Kennan noted that Schiff helped finance revolutionary propaganda during the Russo-Japanese War and Revolution of 1905,[25] through the Society of Friends of Russian Freedom.

When the Nazi Party took power in 1933, the street's name was changed to Mummstraße after Daniel Heinrich Mumm von Schwarzenstein, the city's former mayor, as part of aryanization.