Mr Key said one of the factors that helped New Zealand's success in getting on the council was its record when it was last on the council in 1993-94.
He said that during a visit to New York earlier this year he'd spoken to representatives of African countries.
"The permanent representative from Rwanda stood up and actually said to all the African delegates you have to vote for New Zealand. It's the actions of New Zealand when it was on the council and chairing the council that saved literally millions of people from Rwanda. So it's very serious responsibility and when you do a good job of it that stays in the memory banks for a very long time."
New Zealand's biggest challenge during its new tenure on the council was to work constructively with the five permanent members, Russia, China, the United States, Britain and France who had the right of veto and exercised that right frequently.
"So it's never easy to progress things through the council and you have a combination of this extraordinary responsibility but sometimes it's not always the easiest process to administer."
NZ should maintain independence
Former diplomats Green MP Kennedy Graham and Labour MP Grant Robertson both said it was critical New Zealand maintained an independent foreign policy stance while on the council.
In an apparent reference to the international action against the Islamic State, Mr Robertson said some of Prime Minister John Key's recent comments has raised questions about New Zealand's independent stance on issues the Security Council will need to deal with.
"I urge him to remember our reputation as a peace-keeper and builder and a voice for small countries. This is an amazing opportunity to do the right thing and it must not be wasted."
A former UN diplomat himself, said the Security Council was where all major UN decisions were made and the seat gave New Zealand a rare opportunity to play a part.
"Along with hard work, New Zealand gained this opportunity as a result of our long established reputation as a country that takes an independent stance on the world stage, and that stands up for small states."
Mr Graham, the Green Party's global affairs spokesman, said it was good news for New Zealand, which should use its tenure on the council to try to drive through some much-needed reforms.
"Both the powers and procedural style of the Council are in need of reform. The question of permanent membership, use of the veto, transparency of decision-making and relationship to other international bodies are all in need of review."
He said New Zealand had to adhere to a genuinely independent foreign policy while on the Council.
There are 15 members on the Security Council, five permanent and 10 places among five regional groupings which come up for election every two years.
Other countries elected this morning were Angola, Malaysia and Venezuela. They were the only nomination in their groupings unopposed.
The only group in which there was a contest was the Western European and others grouping.
New Zealand has been a member of the United Nations since it was founded in 1945.
