Saudi Arabia officially joins BRICS bloc: state TV
Saudi Arabia's foreign minister had said in August the kingdom would study the details before the proposed January 1 joining date and take "the appropriate decision".
Prince Faisal bin Farhan had said the BRICS group was "a beneficial and important channel" to strengthen economic cooperation.
The BRICs bloc previously included Brazil, Russia, India, China, and South Africa, but is set to double with Saudi Arabia joining the United Arab Emirates, Egypt, Iran, and Ethiopia as new members.
Saudi Arabia's entry comes amid geopolitical tensions between the US and China and the expansion of China's influence within the kingdom.
Despite continued strong ties with the US, Saudi Arabia has increasingly pursued its own path out of concern that Washington is less committed to the Gulf's security than in the past.
China, Saudi Arabia's biggest oil customer, has led calls for the BRICs to expand to become a counterweight to the West.
The expansion could amplify the group's declared ambition to become a champion of the Global South, although Argentina signalled in November it would not take up an invitation to join.