The six new council members will replace Italy, Japan, Egypt, Senegal, Ukraine and Uruguay
Kuwait was one of six countries elected as non-permanent members of the Security Council for the next two years.
Equatorial Guinea was for the first time elected to the UN Security Council on Friday during a vote that saw Ivory Coast, Kuwait, the Netherlands, Peru and Poland also win seats at the top world table.
The oil-rich central African country, which has been ruled by Teodoro Obiang Nguema Mbasogo for nearly four decades, ran unopposed for one of two seats representing Africa on the council.
The Security Council is made up of 10 non-permanent members elected to two-year terms and five permanent powers: Britain, China, France, Russia and the United States.
The elected countries - all of which were put forward by their regional grouping - will begin their term on January 1.
Human Rights Watch said it had concerns over Equatorial Guinea's role at the council, even if the body is overwhelmingly dominated by the five permanent members.
"They have a long history of harassing, arbitrarily detaining and interfering with the work of human rights defenders," said Louis Charbonneau, HRW's UN director.
Human Rights Watch hopes that "they don't try to obstruct attempts to increasingly integrate human rights defence and the promotion of human rights at the council," he said.
The Netherlands will serve one year at the council under a deal reached with Italy to split the term and break a deadlock over the election.
During the vote at the UN General Assembly, Equatorial Guinea won 185 votes, the Netherlands won 184 votes, Ivory Coast 185, Kuwait 188, Poland 190 and Peru 186.
The six new council members will replace Italy, Japan, Egypt, Senegal, Ukraine and Uruguay.
Diplomats casting at the General Assembly were treated to gifts from candidate-countries: The Netherlands gave stroopwaffels, Ivory Coast handed out coffee and Kuwait offered sweets.