Voronin, who is unable to run for a third consecutive term, was supported by 60 communist lawmakers in the 101-seat legislature. Opposition parties boycotted the vote.
Parliament is due to elect a new president following the parliamentary elections last month. The communists, led by the president, won 60 seats in the assembly, which was one seat short of the 61 needed to secure their presidential candidate.
Voronin urged all MPs, regardless of their party affiliation, to pool their efforts to address the country's outstanding problems.
"We should put our disagreements in parliament behind us and carry out our election mandate, [including] the demand to take down the barricades and build bridges between the different political parties in Moldova," he said.
The opposition has repeatedly stated its refusal to cooperate with the Communists in or outside of parliament.
The Communists' victory in the April 5 election, which gave the ruling party 49.48% of the vote, sparked protests that turned violent in the capital, Chisinau.
Protests originally led by the opposition spiraled out of control when some 10,000 rioters, mainly students, broke into the presidential residence and parliament. Several hundred protesters and police were injured in the violence.
Following the protests the president ordered a recount of election ballots.
A number of opposition parties claimed major violations during the voting and said some 400,000 people had been unlawfully registered to vote.
However, observers from Europe's main election monitoring body, the Organization for Security and Cooperation in Europe, gave their overall endorsement to the voting process.
