Stanislas Saint Clair was born in 1835 in his maternal grandfather's mansion of Vepriai, Vilna Governorate of the Russian Empire (now Ukmergė district of Lithuania), which partially survives to this day.
Brought up with strong Polish identity of his family, he perceived struggle against tsarist Russia as his patriotic duty and this led him to his Balkan activities.
Upon the start of the Russo-Turkish War (1877-78) he formally left British military service and volunteered as an officer in the Ottoman Army under Suleiman Pasha's command, later promoted to the rank of Birindji ferik (General).
Their propaganda efforts aimed to scare Turkish villagers with the rising "rule of the infidels" and make them believe there would soon be retributions for the massacres of Christians during the April Uprising in Bulgaria.
The anti-Bulgarian and anti-Russian nature of Saint Clair's activities soon found the implicit support of the Ottoman and the British empires, both of them hoping to revise the Treaty of San Stefano on terms favourable to Turkey.
After the Treaty of Berlin, the autonomous province of Eastern Rumelia was created and Saint Clair applied for the post of Governor General.
After he learned he was not considered for the post, he retired from political affairs and left for Belgium without achieving the purpose of his ill-fated "insurgency".