In fall 1883, he was invited to teach canon law and the Latin language at the seminary in Kaunas.

He also served as secretary to Mečislovas Leonardas Paliulionis beginning in 1885, where he managed relations with Russian officials.

During his time as bishop of Sejny, he worked to improve the catechization of children and religious education.

After the Sejny Uprising in 1919, Karosas and other Lithuanian clerics were expelled from the town;[3] he stayed at a rectory at Puńsk for some time and in 1920 moved to Marijampolė, where he resided at a Marian monestary.

[3] During World War II, he lived in Vilkaviškis during the Soviet and German occupations of Lithuania, moving to Šunskai in 1944 and back to Marijampolė in 1946.