See biography by S. Kling (1960).
Born to a rabbinic family in Wyszogród, Russia (now Poland), Sokolow began writing for the local Hebrew newspaper, HaTzefirah, when he was only seventeen years old. He quickly won himself a huge following that crossed the boundaries of political and religious affiliation among Polish Jews, from secular intellectuals to anti-Zionist Haredim, and eventually had his own regular column. Over the years, he would eventually become the newspaper's senior editor and a co-owner.
In 1906 Sokolow was asked to become the secretary general of the World Zionist Congress. In the ensuing years, he crisscrossed Europe and North America to promote the Zionist cause. During World War I, he lived in London, where he was a leading advocate for the Balfour Declaration of 1917, in which the British government declared its support for a Jewish homeland in Palestine. In 1931 he was elected President of the World Zionist Congress, and served in that capacity until 1935, when he was succeeded by Chaim Weizmann.
Sokolow was a prolific author and translator. His works include a three-volume history of Baruch Spinoza and his times, and various other biographies. He was the first to translate Theodor Herzl's utopian novel Altneuland into Hebrew, giving it the name Tel Aviv (literally, "Hill of Spring"). In 1909, the name was adopted for the first modern Hebrew-speaking city: Tel Aviv.