Vinaver lived in Saint Petersburg and worked as an assistant to a lawyer on the de facto prohibition of admitting lawyers of Jewish faith as lawyers. During this time he became known as a lawyer by publishing articles in legal journals. Later, he began to develop the defense in criminal cases, resulting from the backward right of the Jews. So he organized in 1900, the successful defense in the Vilna trial of David Blondes, who was charged with ritual murder. After this, he resigned in 1904 in Gomel with a civil suit called the Jewish Victims, accusing the judge of being biased and leaving the trial as the leader of a group of lawyers. It was only in July 1904 that he was sworn in as a lawyer. Winawer lectured on social science at the University of Brussels and at the Paris School of Social Sciences. He became a member of the Legal Society of the University of St. Petersburg and from 1904-1906 headed the civil law department of the editorial office of the newspaper Rechtskurier der Gesellschaft. In 1909 he participated in the editing of the work of the St. Petersburg Legal Society. In 1913-1917 he issued the civil law courier. Vinawer participated in the work of the Society for Education of Russian Jews and became chairman of the Historical and Ethnographic Commission. During the revolution of 1905 he was one of the founders of the Union for Full Rights of the Jewish People in Russia in March 1905, and in 1907 he founded the Jewish Folk Group. He collected paintings and worked as a patron. In particular, he supported Marc Chagall with a small scholarship so that he could travel to Paris in September 1910. In 1905 he was also one of the founders, leaders and theorists of the Constitutional Democratic Party, which was called the party of the Cadets. He became a member of its Central Committee, and he became a deputy in the first State Duma. After the dissolution of the Duma in 1906 he was among the signatories of the Vyborg manifesto. Because of this he was condemned to three months of imprisonment. After the February Revolution, Winawer joined the Working Group on drafting laws for the election of a Constituent Assembly, and the Provisional Government appointed him Senator of the Civil Division of the Senate Court of Cassation. He was a member of the new Central Duma. During this time he tended to the left wing of the Cadet Party, and he was Deputy Group Chairman in the Provisional Soviet of the Russian Republic. In 1917 he was elected to the Constituent Assembly of Petrograd. From March 1917 he was the Head of the Commission for Agitation and Publication of the Cadets Party together with the historian Alexander Alexandrovich Kornilov. He was also one of the editors of the newspaper Kurier of the People's Liberty Party. Even before the October Revolution and after an illegal stay in Moscow, Winawer fled to Crimea and took part in the conference of the Cadets on 1 October 1918 in Gaspra. In the spring of 1919 he became Foreign Minister of the Regional Crimean Government, which turned against the Bolsheviks to the Entente Powers. In 1919, Winawer emigrated to France and settled in Paris, where he called on the allies of Russia to continue to support the White movement. He was a friend of the Chairman of the Committee of the Paris Group of Cadets and joined the unification of all democratic forces of the emigrants. He was chairman of the Russian Publishing Society in Paris, one of the founders of the Russian newspaper Recent News and initiator of the construction of a Russian university at the Sorbonne, where he gave a lecture on Russian civil law. He participated in the publication of the newspaper Jewish Tribune that fought against anti-Semitism. He played a large part in the trial of Scholom Schwartzbard, who had shot in 1926 in Paris the former Ukrainian President Symon Petljura, and was scheduled as a witness of the defense.
