As part of the deal, which amounts to a takeover by PropertyPal as the larger business, the websites will continue to operate separately.
A spokesman said the merger would mean better value and improved services for agents and website users.
It comes after some estate agents boycotted PropertyPal earlier this year over an increase in its fees.
The spokesman said there would be significant investment in marketing both platforms, as well as upgrading technology infrastructure and improving the software used by agents.
Jordan Buchanan, CEO of PropertyPal, said: “This merger is very positive for our people, our customers, and our website users.
“We are bringing together the best of our technology, people, and cultures to create something even better. Our aim is to enhance the value we offer to consumers and agent partners alike.”
He added: “By combining our resources and expertise, we will deliver more efficient, cost-effective, and user-friendly platforms.
“Our commitment to innovation and customer satisfaction remains at the core of everything we do, and I am confident that this merger will drive forward our vision of providing exceptional service and support to the Northern Ireland property market. We look forward to working closely with our agents and stakeholders during this exciting transition and beyond.”
GCD Technologies, former owner of Propertynews, becomes a shareholder of the parent company, PropertyPal.
Andrew Gough, GCD managing director, will join PropertyPal’s board of directors.
The new board will also include Conor MacCarrick, former board member of Propertynews, and Jordan Buchanan, CEO of PropertyPal.
They will join the existing team, including chairman Cecil Hetherington and founder Errol Maxwell, to work alongside the management team.
Emma McNally, commercial director at Propertynews, will step into the role of chief operating officer at PropertyPal.
Ms McNally said: “This is a significant milestone for both websites. Through a united approach, we will strengthen our offerings to drive growth and innovation.
“By combining our technical, commercial, and sector expertise, we will deliver a best-in-class user experience and create additional value for our customers.
“I am eager to engage with our expanded team and valued business partners to achieve our shared vision for success.”