WhatsApp tested the payment system in India beginning in 2018. The Brazil launch will be the first nationwide rollout and will introduce the ability to directly pay a business.
The company has over 120 million individual users in Brazil, its second-largest market behind India.
"WhatsApp is heavily used there, both by people and small businesses," Matt Idema, chief operating officer of WhatsApp, said of Brazil.
"We think we can help grow digital payments, help grow the digital economy with small businesses, and help support financial inclusion," he told Reuters in an interview.
Many of Brazil's small businesses already use WhatsApp as a marketing tool to answer questions or send catalogs, Idema said.
Facebook Chief Executive Mark Zuckerberg said in April that the company was expanding tools for businesses in WhatsApp.
The rollout in Brazil was long planned, but may help users who are shut in during the coronavirus pandemic, Idema said.
"We can't have the kind of interactions with each other that we normally would, if you want to lend someone cash or if you want to buy something from a local business," he said.
The payment system will use Facebook Pay and be free to individual users, while charging businesses a fee for receiving payments.
Initially, the system will accept payments from debit and credit cards from Banco do Brasil, Nubank and Sicredi, and is working with Cielo to process the payments.
Idema said the company was planning to bring the payment system to several other countries, but he did not specify which ones.