As voivode, he signed the election of Stanisław II Augustus in 1764, and was later an envoy to the Repnin Sejm. Because of his opposition to the Russian ambassador there, he and his father, Wacław Rzewuski were kidnapped on the night of 13/14 October 1767 by Russian forces under the command of General Iosif Igelström and imprisoned in Kaluga. He returned to Poland in 1773. On 4 September 1775, both received in restitution from the king the Orders of St. Stanislaus and the White Eagle, but this was not enough to reconcile Seweryn, who blamed Poniatowski for his ordeal.