Bronisław Euzebiusz Wesołowski (14 August 1870 – 2 January 1919) was a Polish communist revolutionary and labor leader.

A Pole, born in a village near Warsaw, he became a committed socialist while in his teens. In 1889, together with Adolf Warski and Julian Marchlewski, he founded the Union of Polish Workers^[1] He studied at Zurich Polytechnic. In 1893, the Union was disbanded and its members joined the Social Democracy of the Kingdom of Poland (SDPK - later the SDPKiL), founded in Zurich by Rosa Luxemburg and Leo Jogiches. Wesolowski returned to Poland, and was the only member of the Zurich-based leadership to attend the founding congress of the SDPK in March 1894.^[2] He was arrested soon afterwards, and spent more than ten years in Siberia. Released during the 1905 revolution, he returned illegally to Warsaw, where he was arrested again in 1908. After another nine years in prison and exile, he was released after the February Revolution, in 1917, and joined the Bolsheviks.

On 20 December 1918, Wesolowski arrived in Warsaw as head of a five-member Soviet Red Cross mission, to discuss the repatriation of former Russian prisoners of war, who had bene held in Poland by the Germans during World War I. All five were arrested by the Polish authorities, who suspected that they had come to spread communist propaganda, and were expelled from Poland. Near the border with Soviet Russia, on the night of 1/2 January 1919, they were seized by Polish gendarmes, taken to a wood and shot. Wesolowski and three others were killed, while one member of the delegation survived by pretending to be dead.^[3]