Solicitor Paul Tweed said he would stay on as partner after his firm was acquired by London-listed legal services group Gateley for £2m (€2.3m).
A high-profile lawyer who specialises in defamation, media and arbitration, Mr Tweed has defended a raft of major international celebrities.
They have included the likes of Britney Spears, Liam Neeson, Nicholas Cage and Jennifer Lopez.
Mr Tweed's business currently has offices in Belfast, Dublin and London.
Gateley said the deal would provide it with a platform for growth across the island of Ireland. Mr Tweed has said he will remain as a partner in Gateley Tweed.
"It will be very much as before but we will have the strength of Gateley behind us," he said. "They are a full-service law firm and one of the biggest in the UK, so it will give us a lot more back-up."
He said that Selena Kerins, also a partner in Tweed Law, will remain as well and that the business will look to expand.
"We will be offering more legal services, and Gateley will bring in the people with the expertise for that," he said .
"They will be recruiting locally, though I will still be doing what I'm doing at the minute."
"We have considered expanding into the Irish market for some time and Tweed strengthens our presence in the Irish professional services market," said Gateley CEO Michael Ward.
"We see this as a springboard for developing a strong legal services offering in Ireland, as well as supporting our growth plans for Gateley Capitus."
Gateley Capitus specialises in advice to clients on tax incentives available for investment in commercial property, and R&D activities.
Mr Tweed left Johnsons Solicitors in 2017 to establish his own law firm.