The five will join the 15-nation body responsible for maintaining international peace and security on Jan. 1, 2020.
There is usually little suspense in the General Assembly for the vote, as regional groups typically pre-select a candidate from within their bloc to run uncontested. This year, Tunisia, Niger and Vietnam ran unopposed.
So did Saint Vincent and the Grenadines, until just hours before Friday morning's vote, when El Salvador announced it would challenge the tiny island nation for the one open seat in the Latin American and Caribbean region.
Diplomats expressed surprise ahead of the vote as to why El Salvador would come in at the last minute, when the regional bloc had agreed in December to put up Saint Vincent as their candidate.
"You don't do it like that," one western diplomat said disapprovingly.
Most other countries appeared to agree, with El Salvador winning only six of the 193 votes cast.
Eastern Europe did run a contested race this year, endorsing two candidates, Estonia and Romania.
Estonia, which joined the U.N. in 1991 after the collapse of the Soviet Union, has never served on the Security Council. It beat four-time council veteran Romania after two rounds of ballots, exceeding the necessary two-thirds majority needed.
Member states cast secret ballots and candidates must win a two-thirds majority of votes to succeed, even if they are running uncontested. Candidate countries cap off their often years-long campaigns with parties in the lead-up to the vote.
"I want to reiterate that Saint Vincent and the Grenadines views this as an historic occasion," Prime Minister Ralph Gonsalves told reporters after the election. "We are the smallest country ever to be elected as a non-permanent member of the Security Council."
The island nation has a population of just 110,000.
Saint Vincent and the Grenadines has aligned with the Maduro regime in Venezuela.
"Non-interference, non-intervention, peaceful settlement of serious difficulties pertaining to governance," the prime minister said when asked what his government's policy is toward Venezuela.
Vietnam had nearly unanimous support in the General Assembly, winning 192 of 193 votes.
"As Vietnam went through decades of war, we hope that we can bring to the council the experience of Vietnam, the country that has been able to rebuild after the war and deal with many other issues," said the president's special envoy Le Hoai Trung.
Tunisian Foreign Minister Khemaies Jhinaoui said his nation would try to be a "bridge builder" on the council and contribute to trying to solve some of the most important peace and security issues.
"With the election of Saint Vincent and Vietnam, the Security Council could tilt a little towards China and Russia next year," said Richard Gowan, U.N. Director, International Crisis Group. "Saint Vincent has stuck with Maduro in Venezuela, and Vietnam hews to a pretty robust anti-Western line in U.N. debates."
Tunisia and Niger will represent Africa on the council. Gowan told VOA they could figure prominently if Libya and the Sahel continue atop the agenda.
"It will be hard to ignore their views on issues like the spillover of violence from Libya and the worsening security situation in Burkina Faso," he said.
The five new council members will replace Cote d'Ivoire, Equatorial Guinea, Kuwait, Peru and Poland, whose terms end Dec. 31, 2019.
They will join the other non-permanent members — Belgium, the Dominican Republic, Germany, Indonesia, and South Africa — as well as the permanent five members — Britain, China, France, Russia and the United States.