Jacob Pat was born in Bialystok, Russian Empire, in 1890. He attended yeshivas in Slobodka and Slutek and later graduated from a teachers' seminary in Vilna. Active in the Zionist-Socialist Workers Party from 1905, he dropped his Zionist sympathies and became a member of the social-democratic Jewish Labor Bund after World War I. While working as a teacher, he also served as secretary of the Jewish Community Board of Bialystok, 1917-1920. He lived in Warsaw from 1921 to 1938, and worked there as General Secretary of the Bund's Central Association of Yiddish Schools (CISHO), which enrolled an estimated 60,000 children throughout Poland during the interwar years. He was a prolific journalist, editing and writing for Bundist children's magazines, and serving as co-editor for the Polish Bund's newspaper, the Folkstseitung.

In the 1930s he traveled to the United States on fund-raising trips, representing the Bund schools. One such trip took him to New York City in the fall of 1938. Worsening conditions in Europe forced him to remain in the United States to devote himself to anti-Nazi activity and rescue work. He had left behind in Warsaw his wife, Rivke Pat, and two children, Emanuel and Naomi. The family fled to Vilna after the German invasion of Poland, and there Rivke Pat died. Emanuel and Naomi Patt (this spelling of the surname was adopted by them in the U.S.) were brought to the U.S. on special visas in 1940. Jacob Pat remarried, to Frieda Wider, in 1942.

In 1941 Pat became Executive Secretary of the Jewish Labor Committee, a position he held until his retirement in 1963. He also served as a member of the Delegation of the Jewish Labor Bund to the U.S., 1938-1947, as chairman of the Congress for Jewish Culture, and as co-editor of Zukunft. In 1946 he toured displaced persons camps and visited with communities of Jewish survivors in France and Eastern Europe; he wrote about his experiences in Poland in Ashes and Fire(1947). In later years he traveled extensively to Europe, South America and Israel. He was a frequent contributor to the Jewish press both in Yiddish and English, and published a number of books, including Conversations with Jewish Writers (1959). He died in New York City on April 26, 1966.