The news comes after NAB Asset Servicing announced on the ASX in July 2014 that it is in discussions with a number of global custody providers about the future of its business.
In a joint statement with AUI, BNP Paribas said the appointment came after an "extensive market review".
AUI chief executive David Bryant said BNP Paribas was determined to have the "strongest full service proposition in core custody, together with middle and back office services for our asset management business and joint venture partners".
"BNP Paribas was also able to demonstrate a strong leadership team with a great deal of local autonomy," Mr Bryant said.
"We were also most attracted to BNP Paribas’ ongoing investments in technology and their commitment to supporting our expansion plans, and in turn, helping us to future-proof our strategy," he said.
A statement by BNP Paribas Securities Services hailed the appointment as a "significant and strategic win" that demonstrates the firm's "growing presence" in the Melbourne market.
"Our commitment to Australian Unity Investments and to all of our clients is to partner with them to optimise their operational processes, minimise their risks and enhance their performance wherever possible," BNP Paribas said.
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