He was close to Stanislaus Czerniewicz and Lenkiewicz, and helped them in their efforts to keep the Society of Jesus going in Russia. He was made the Rector of the High School of Orsha in 1782 and took part in the Regional Congregation of 1782 and 1785 that elected successively Cerniewicz and Lenkiewic as vicars general of the Jesuits. After 1785, Kareu was made Rector of the most prestigious Jesuit College in Russia, Polatsk. In this period, he funded the purchase of a printing press from which, school manuals, philosophical and theological treatises and devotional books were produced.
He was elected Vicar General in 1799, and was to witness the partial restoration of the Society with the publication of the Papal Brief Catholicae Fidei. Kareu suffered from asthma. When he realised that his health had become a liability, he appointed a Vicar General to assist him as. He died in Polatsk on 11 August 1802.