A subsidiary of mortgage administrator HML has agreed to buy mortgage servicing company Topaz Finance from Ulster Bank parent RBS.
The value of the transaction was not disclosed and the deal is subject to regulatory approval.
Topaz - which is not connected to Topaz garages - has a £700m portfolio of mortgages.
The HML subsidiary - Specialist Mortgage Services (SMS) - is a mortgage manager that seeks to optimise a mortgage portfolio's performance on behalf of the portfolio's beneficial owners.
"With the recent improvements in the economy, momentum for trading mortgage portfolios is building quickly," SMS managing director Andrew Freeley said.
"Our clients are increasingly looking for a strategic partner who specialises in managing mortgage portfolios to support their acquisition and disposal strategies, to enhance the value of their mortgage assets and to provide the rigour and quality required to manage customers and regulatory risk effectively."
"The acquisition of Topaz supports our strategy, giving us further scale and enhanced capability in mortgage portfolio management," Mr Freeley added.
HML has around £37bn in managed assets and 50 major clients - including banks and building societies.
It was bought by Australian financial services company Computershare last year for an upfront payment of £47.5m, plus add ons.
HML chief executive Andrew Jones said the Topaz acquisition is an important part of Computershare's "significant" plan to grow HML's loan servicing business.
"The growth of SMS is integral to both Computershare and HML's strategy for 2015 and beyond. We have already benefited from working with our new parent's US mortgage administration company," Mr Jones added.
"Further investment into our market-leading advanced analytics and technology will enable us to continue our growth plans," he said.