This will bring to eight the total number of the LSDP group members.
Balsys confirmed to BNS that he is joining the LSDP group, saying that this will help him to better realize his political ideas.
The lawmaker said that he chose the LSDP group because they are ideologically close to him, but underlined that he is staying in his Lithuanian Green Party.
LSDP leader Gintautas Paluckas is confident that a scandal over suspected drunk-driving by Balsys will not harm the political group's reputation.
Balsys last November agreed to blow into a breathalyzer device, producing a reading of 1.82 per mille of alcohol, and left the Seimas building in his car shortly afterwards.
Law-enforcement officials launched a probe into a suspected drunk-driving incident, but later closed it due to insufficient evidence.
Balsys returned to work more than a month later, saying that he had undergone medical treatment.
Paluckas said that "dependence on alcohol is a disease", adding that the Social Democrats are ready to give a helping hand to anyone who needs it.
LSDP struggled to keep its political group in the Seimas after a number of breakaway members last year registered a new Lithuanian Social Democratic Labor political group.
LSDP last October registered a new political group in the parliament, having reached the required minimum number of seven after MP Dovilė Šakalienė joined it.