Saudi state TV said on Tuesday that the kingdom had officially joined the BRICS bloc of countries.
Saudi Arabia's foreign minister had said in August the kingdom would study the details before the proposed Jan. 1 joining date and take "the appropriate decision."
Prince Faisal bin Farhan Al Saud 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 U.S. and China, and the expansion of China's influence within the kingdom.
Despite continued strong ties with the U.S., 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" developing nations, although Argentina signaled in November it would not take up an invitation to join.