Applause rang out at the assembly hall after Sweden's victory was announced.
Swedish Foreign Minister Margot Wallström said she was “happy and proud” to see her country join the UN's top table, pledging to focus firmly on conflict resolution.
“With 40 conflicts and 11 full-blown wars, it is a very, very worrisome world that we have to take into account,” Wallström said.
Bolivia, Ethiopia, Kazakhstan and Sweden were elected on Tuesday to serve a two-year stint on the
UN Security Council, with the Netherlands and Italy locked in a tight race for a remaining spot.
Five non-permanent seats are up for grabs in the vote by the UN General Assembly, three of which were filled in a first round of secret ballot voting.
After the first round, Kazakhstan was ahead with 113 votes compared to 77 for Thailand, but the central Asian country fell short of the two-thirds majority required to win election to the seat reserved for Asia.
Among the world's top aid donors, Sweden picked up 134 votes, scoring an outright win, while the Netherlands garnered 125 votes and Italy 113, falling short of the required majority.
The five new elected countries will take their place alongside the five permanent council members — Britain, France, China, Russia and the United States.
The other five non-permanent members are: Egypt, Japan, Senegal, Ukraine and Uruguay.
Ethiopia picked up 185 votes, running unopposed as the candidate from Africa.
With some 8,100 troops deployed in UN missions, Ethiopia is the largest contributor of UN peacekeepers and has been active in trying to mediate an end the war in South Sudan.
Bolivia, which had the backing of Latin American and Caribbean countries, won 183 votes.
On the eve of the vote, Human Rights Watch called on UN member-states to closely scrutinize the human rights record of Kazakhstan and Thailand.
Thailand's military junta, which seized power in May 2014, has banned political activity and ramped up prosecutions under tough sedition and royal defamation laws.
Vying for a council seat for the first time since its 1991 independence from the Soviet Union, Kazakhstan has been criticized for cracking down on journalists and political activists.
“Debate happens in UN corridors in New York in a way that is not allowed in Kazakhstan itself,” said Philippe Bolopion, a deputy director at HRW.
Italy has lobbied fiercely for a council seat, portraying itself as a crossroads country in the Mediterranean and touting its experience dealing with the refugee crisis.
Italy is also seen as a player in efforts to pull Libya out of chaos.
The Netherlands, home to the International Criminal Court and other world tribunals, has played up its commitment to international justice.
The vote for a seat at the top diplomatic table caps years of lobbying by contenders.
As the ballot got underway, delegates at the 193-nation General Assembly were handed gift bags with miniature tulips and wooden shoes from the Netherlands, Baci chocolates from Italy and a buddha figurine from Thailand.