Butkevičius was the only candidate in the election after MEP Zigmantas Balčytis withdrew his candidacy during Saturday's congress.
The party's leader is elected in a secret ballot during the congress every two years. Under the Lithuanian Social Democratic Party's statute, candidates for party leadership are required to have three years of uninterrupted party membership.
Butkevičius was first elected as the leader of the Social Democratic Party in 2009 and won reelection for another two years in 2011. Two years ago, Butkevičius had no opponents in the race and was supported by 541 out of 589 members.
In the 2012 parliamentary elections, the Social Democrats won more seats - 40 - than any other party in the Lithuanian parliament and subsequently formed the ruling center-left coalition with the Labor Party, the Order and Justice party, and the Electoral Action of Poles in Lithuania.
According to data published by the Justice Ministry, the Social Democratic Party is the largest in Lithuania with 17,972 members.
