 Nothing is known about the youth of Vaišvilkas as he entered historical sources only in 1254 when he made a treaty, in the name of his father King Mindaugas, with Daniel of Halych-Volhynia.In the treaty, Halych-Volhynia transfers Black Ruthenia with center in Navahrudak to Lithuania.To solidify the treaty, Daniel's son Shvarn was married to Vaišvilkas' sister.