Davy, which said it is eyeing further targets for acquisition in the province, paid an undisclosed sum for Square Seven.
The Castlereagh Road-based business was founded in 2005 by David Rea and Sam Curry to advise private, corporate, trust and pension clients.
The two will now join Davy's existing private client team of 10 advisers in their offices in Donegall Square.
Stephen Felle, managing director of Davy Private Clients (NI), said: "Davy has experienced strong growth from our Northern Ireland business, particularly over the past two years.
"Senior appointments at our Belfast office, together with the acquisition of Square Seven, firmly establish Davy as a major player in Northern Ireland's evolving financial services marketplace."
He said the business had grown its assets under management by over 20% during 2013. "Additionally, our Belfast office was last year awarded the tender for one of the largest public service investment management contracts in Northern Ireland," he said.
"Northern Ireland is a material part of Davy's overall private client business, and we see it as an area of key strategic growth in the coming years. We will continue to review further potential acquisitions in Northern Ireland such as that offered by Square Seven."
And Mr Felle said its position in Northern Ireland also opened up access to the rest of the UK.
In a statement, David Rea and Sam Curry said: "We are proud of the business we have created in Square Seven over the past eight years and we are extremely appreciative for the support of our clients and staff in this regard. Having conducted a thorough review of our expanding business and client needs, we concluded that it was in the best interests of our clients to strengthen our offering and join with a larger organisation.
"In selecting Davy we are joining Square Seven with a firm that has the requisite financial and infrastructural resources to meet our clients' evolving requirements in the years ahead."
Square Seven is understood to have around 400 clients, with over £74m worth of assets under management.
Davy last year won a tender from the Northern Ireland Courts and Tribunals Service to manage and invest the funds held in court on behalf of its clients. The funds are estimated at £300m.
Square Seven is Davy's second acquisition this month after buying investment consultancy iCubed.