Citi said there would be no immediate change to the way it served its customers, with more details given to them in the coming months.
Subject to how long approval from regulators takes, the deal is thought to be completed by March next year.
The deal is reportedly worth $1.2 billion, with NAB stating it was paying the Citigroup cash for the assets, plus $250 million as a sweetener.
In July NAB announced to the Australian Securities Exchange it was an interested buyer.
Citi's Australian consumer assets total approximately $12.2 billion and include $7.9 billion in residential mortgages, $9 billion in deposits, and $4.3 billion in unsecured lending.
Citi also employs 800 people in Australia, who will be absorbed into NAB once the transaction has been finalised.
NAB chief executive, Ross McEwan, said Citi had built strong partnerships across many brands, which would help support the big four lender's growth moving forward.
"The proposed acquisition of the Citigroup consumer business brings scale and deep expertise in unsecured lending, particularly credit cards, which continue to be an important way for customers to make payments and manage their cashflows," Mr McEwan said.
"The cards and payments sector is rapidly evolving and access to a greater share of payments and transaction data will help drive product and service innovation across our personal banking business and deliver market leading customer experiences."
Citi is a credit card provider for a number of Australian brands, including Bank of Queensland, Coles, Kogan, PayPal, QANTAS, Suncorp, and Virgin Money.
Only last week Citi announced its new buy now, pay later platform called Spot, with no news yet as to how the sale will affect the venture.
However, Citi's head of cards and loans, Choong Yu Lum, last week told Savings.com.au: "Typically, in transactions like these, products will migrate to the new owner once the sale has been completed."
Citi chief executive, Marc Luet, said the sale to NAB was a positive outcome for the bank, its customers, and its clients.
"The sale agreement furthers Citi’s global strategy of focusing its resources on businesses that can drive stronger growth, deliver scale and enhance returns, which includes our Institutional Clients Group businesses in Australia," Mr Luet said.
"Citi has been in Australia for close to a century and it remains an important growth market for the bank."
Citi announced in April it would be pulling out of Australian consumer banking, with the intention to focus solely on investment banking.
Citi's Securities Services business holds more than $23 trillion in assets with a network spanning 64 markets, and is ranked third in Australia by assets under custody for local investors.
Earlier in the year, regulators approved NAB's acquisition of neobank 86 400.
Photo by Mikel Parera on Unsplash
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