 Tamkevičius was appointed auxiliary bishop of Kaunas on 8 May 1991 and was consecrated a bishop on 19 May 1991.Pope John Paul II appointed him Archbishop of Kaunas on 4 May 1996.Within the Lithuanian Episcopal Conference, he has been President (1999–2002, 2005–2008, and 2008–2014) and Vice-President (2002–2005).