Landman was born in Russia on October 4, 1880 to Ada and Louis Landman. He emigrated to the United States in 1890. He graduated from the Reform Hebrew Union College. In 1911, with the assistance of Jacob Schiff, Julius Rosenwald, and Simon Bamberger, he founded a Jewish farm colony in Utah. In 1913 he married Beatrice Eschner. During World War I he was "said to be the first Jewish chaplain in the United States Army to serve on foreign soil".
He was a leader in Jewish–Christian ecumenism. He was editor of American Hebrew Magazine from 1918, served as the delegate of the Union of American Hebrew Congregations to the 1919 Paris Peace Conference.
Landman had also been a prominent opponent of Zionism: when, in 1922, the United States Congress was considering the Lodge–Fish resolution in support of the Balfour Declaration, Landman and Rabbi David Philipson had presented the Reform movement's (then) anti-Zionist position to the House Committee on Foreign Affairs. Landman also printed many opinions against the resolution and Zionism in his American Hebrew Magazine. The bill was eventually unanimously supported by both houses of Congress, and approved by President Harding.
He became rabbi of Brooklyn's Congregation Beth Elohim in 1931. Three years later he began editing the Universal Jewish Encyclopedia, which was published in ten volumes in the 1940s. He died on September 4, 1946.
- "Isaac Landman Papers". University of Illinois at Chicago. Retrieved 2011-04-21. "Isaac Landman, rabbi and journalist, was born in Russia in 1880 and was brought to the United States at the age of ten. He was ordained a Rabbi at the Hebrew Union College in 1906. On March 24, 1909, Rabbi Landman delivered "The Call of the Farm" address at Hull-House. In 1911, with the aid of Jacob H. Schiff, Julius Rosenwald, and Simon Bamberger, Rabbi Landman founded a Jewish farm colony in Utah. ..."
- "Jewish Editor Will Also Be Rabbi of a Brooklyn Congregation". New York Times. May 30, 1931. "Isaac Landman, editor of The American Hebrew and editor-in-chief of The Standard Jewish Encyclopedia, will return to the active ministry as rabbi of ..."
- "Rabbi Landman, 65, Reformist is Dead. Brooklyn Preacher a Leader in Hebrew-Christian Moves for Religious Friendship". New York Times. September 5, 1946. "Rabbi Isaac Landman of Congregation Beth Elohim, Brooklyn, president-elect of the Synagogue Council of America, editor of the Universal Jewish Encyclopedia, director of the Academy for Adult Jewish Education and former editor of The American Hebrew, died ..."
- Cohen, Naomi W. The Americanization of Zionism, 1897-1948, University Press of New England, 2003, p. 68. ISBN 978-1-58465-346-2
- Reich, Bernard, "The United States and Israel: The Nature of a Special Relationship", in Lesch, David W. The Middle East and the United States: A Historical and Political Reassessment (Fourth edition), Westview Press, 2007, p. 206. ISBN 978-0-8133-4349-5
- "Zion, Ten Years After". Time magazine. April 4, 1932. "Last week's money-gathering began importantly. Any Jew could be impressed by the following facts: Anniversary, Ten years ago next May the Lodge-Fish resolution, favoring the Jewish National Home, was introduced in Congress. In September it was approved by President Harding, became a public resolution."