In 1914, he moved to
Kraków and joined the
First Cadre Company, which fought on the
Austro-Hungarian side against
Russia. In October 1914 he became a commander of a platoon of a squadron in
1st Uhlans Regiment of Polish Legions. During the fighting in 1914–1915, he was promoted to lieutenant, and after the war he was awarded the V-Class
Virtuti Militari. In August 1915, he moved to the special group in Warsaw. Soon he became an aide-de-camp to
Józef Piłsudski. In 1918, he was sent on a mission to Russia. He was given three tasks: persuade General
Józef Haller's army, then in the Ukraine, to back Piłsudski (he failed in this task); reach the French military mission in Moscow under General Lavergne (he succeeded in this task); and return from Moscow to Paris to liaise with the government there. Unfortunately, he was arrested by the
Soviet Cheka as a member of the
Polish Military Organisation while on a French diplomatic train on its way from Moscow to
Murmansk (and Paris). He was imprisoned in the
Taganka prison. He was freed thanks to the intervention of his future wife,
Bronisława Wieniawa-Długoszowska, with the much-feared
Cheka operative
Yakovleva, then in charge of the prison. Bronisława, née Kliatchkin, was at that time married to the lawyer , the lawyer of
Felix Dzerzhinsky, the head of the Cheka. She was a Lutheran, her family having converted from the Jewish faith when she was eight. He married her in a Lutheran ceremony on 2 October 1919 at '''' in
Nowy Gawłów. The marriage register records the details from her false French passport, including "Lalande" as her maiden name. As aide-de-camp of
Józef Piłsudski during the
Polish-Soviet War he helped him organize the
Vilna Operation and
Battle of Warsaw. He was also a commander of 1st Cavalry Division. After the war, Wieniawa was awarded many medals (including the
Légion d'honneur,
Cross of Valor and
Cross of Independence). Throughout the interwar years, he was a key figure in Warsaw literary and social life. He had a table reserved for him with leading Warsaw literary figures, such as
Julian Tuwim and
Jan Lechoń, at the mezzanine of the café . In a famous anecdote,
Aleksander Wat recounts how, when Wat was imprisoned, by the government of the
Second Polish Republic for his literary activities (he was the publisher of the
crypto-communist magazine ), he received, in prison, a hamper of vodka and caviar from Wieniawa. The purpose of that story, in Wat's memoirs "My century", is to contrast his treatment at the hands of the
Second Polish Republic with the vicious and barbaric treatment he was to receive in Soviet prisons during the war. In November 1921, Wieniawa became the Polish military attaché in
Bucharest,
Romania. He was associated with making the Polish-Romanian convention which was signed in 1922. In 1926 he passed his exams in High War School. He soon became a commander of , the most prestigious and representative Polish cavalry division, which he commanded until 1930. During the
May Coup of 1926, he was one of Piłsudski's officers who helped him to organise the coup. In 1930–32, he was commander of I Cavalry Division and, for some time, of II Cavalry Division. In 1932, he was promoted by President
Ignacy Mościcki to the rank of . He was commander of the , from 1932 to 14 May 1938. In 1938 he was promoted to Major-General, . From 1938 to 13 June 1940, he was the Polish Ambassador in
Rome. == One-day presidency ==