Premier Miton Group announced it had assets under management of £11.1bn at the end of October after a "difficult" year.
The company, which was formed by the merger of Premier and Miton, said the deal would give it "greater financial strength to grow".
Mike O'Shea, Premier Miton's chief executive, said: "The merger will create a diversified active UK asset manager with a strong investment capability that benefits from a more efficient platform and greater financial strength, with combined AUM of £11.1bn.
"Premier Miton's blend of outcome-based multi-asset strategies and genuinely active single strategies, run by highly regarded teams, and supported by enhanced distribution is a unique proposition, which we believe will be highly attractive for advisers and wealth managers."
At the same time the company announced the results of Premier for the year to the end of September, which showed its assets under management fell from £6.9bn to £6.6bn over the year.
It saw net outflows of £233m in the year to September compared to net inflows of £734m in the previous year.
Mr O'Shea, who was chief executive of Premier until become head of the merged company, said: "This has been a more difficult year for the business and indeed for the UK funds industry generally, with investment decisions largely on hold while investors wait for clarity over Brexit.
"As confidence returns to the UK market, we believe that our focus on delivering good client outcomes and our relevant product range mean we are well placed for future growth."
In October Miton announced it had assets under management of £4.6bn and had also seen net outflows - of £121m.