The two parties merged into one legal entity on Wednesday night. The party's press center told BNS that Gapšys, 31, was unanimously elected chairman of the new party.
Uspaskich had said on numerous occasions that the party merger had nothing to do with the trial of the Labor Party on fraud charges. The new party will assume all duties and responsibility of the old one, Uspaskich said.
Meanwhile prosecutor Saulius Verseckas has said that everything will depend on the conditions and model of the merger.
The Labor Party is on trial for failing to include more than 24 million litas (EUR 6.9m) in income and 23 million litas in spending in its books in the 2004-2006 period. Charges have been brought against its leader Uspaskich, his deputy Gapšys, MP Vitalija Vonžutaitė, and the party's former accountant Marina Liutkevičienė.
Uspaskich rejects all charges and says the case is politically-motivated.
Prime minister welcomes merger
Lithuanian Prime Minister Algirdas Butkevičius has welcomed the news that the Labor Party, one of the parties in his coalition, merged with non-influential Laborist Party, and called talks that it might be an attempt to evade prosecution "politicizing."
"I really don't know what the motives are but I welcome this merger as I believe there should be as few parties in Lithuania as possible. The bigger parties are, the easier it is for the public to make up its mind which party to vote for, and that party's role in the political life will grow," the prime minister told the Žinių Radijas (News Radio) on Thursday.
Asked about political scientists' opinion that this way the Labor Party is trying to evade prosecution in a fraudulent bookkeeping case, Butkevičius called it politicizing.
"I believe it's a big party and it's fully responsible for its actions and it has a future vision," he said.
"The new party will assume all responsibilities and duties which might remain after the merger. Under the merger conditions, members of the Labor Party and Laborist Party will automatically become members of the [new] Labor Party. The new party will have 17,380 members," the Labor Party's press center said in a statement.