The completion follows Standard Life Aberdeen’s announcement it would be selling the business after the merger between insurer Standard Life and asset manager Aberdeen last year.
As part of the deal Standard Life Aberdeen will acquire a shareholding of just under 20 per cent of the wider Phoenix Group.
Standard Life Aberdeen will retain it three adviser platforms, Wrap, Elevate and Parmenion, as well as its advice business 1825 which have £58bn of assets under administration.
The buy-out will see an expansion of the long-term partnership between the two businesses, and Standard Life Aberdeen will aim to grow the business through targeted investments.
Sir Gerry Grimstone, chairman of Standard Life Aberdeen, said: "This is a momentous day for Standard Life Aberdeen as we continue to build a world-class investment company.
"Corporate transformations of this scale require clear vision and huge commitment from all those involved. Maintaining continuity of service and enhancing optionality for all our customers and clients has been a key imperative. My very best wishes for the future to all our employees and customers who are transferring to Phoenix."
In May Standard Life Aberdeen announced a proposed capital return to shareholders of up to £1.75bn, with £1bn to be returned to shareholders and the remaining up to £750 million to be returned by way of a share buyback programme.
The sale comes after Scottish Widows, Standard Life Aberdeens largest client, withdrew £109bn of assets of from the company as part of a review of its long-term asset management arrangements.
Months after Scottish Widows withdrew its assets, Lloyds Banking Group cut ties with Standard Life Aberdeen due to concerns that Aberdeen Asset Management had become a competitor, following its merger with Standard Life.