Listed recruitment firm Staffline - led in Ireland by former NI21 candidate Tina McKenzie - has acquired Diamond Recruitment in Belfast for an undisclosed sum.
A spokeswoman said more acquisitions could follow in Ireland for Staffline, which set up an Ireland division in 2013.
Diamond Recruitment, which is based in Belfast city centre, specialises in temporary and permanent recruitment.
Staffline said Diamond brought a number of "large blue-chip clients" on its books and had an "excellent reputation".
It said that Diamond Recruitment places 2,750 people under contracts of employment for clients in food, manufacturing and IT sector.
Staffline's clients are concentrated in logistics, food and office administration.
The acquisition means that Staffline Group Ireland now has 10 sites with over 3,000 contractors available for work with hundreds of clients.
Tina McKenzie said: "We're happy to welcome the Diamond team to Staffline Group Ireland. "This acquisition fits our strategy of selective bolt-on acquisitions and enhances our reach and customer base considerably across Northern Ireland.
"Combining Staffline Recruitment, PeoplePlus NI and Diamond, we will ensure that local employers have a wider range of services available to them while jobseekers, learners and staff have a greater choice of career opportunities."
Workers have permanent contracts with Diamond under Agency Workers Regulations (AWR).
The spokeswoman said Staffline Group Ireland had grown from a staff of two in 2013 to a staff of 120 at present.
"We established in Belfast in 2013 under Tina's direction and have grown since then to a turnover of £55m in 2015."
She said the purchase price could not be disclosed.
Michael Johnston, managing partner at Carson McDowell, acted on behalf of Diamond Recruitment in the deal.
He said: "This transaction demonstrates yet again that high quality Northern Ireland companies are very much on the radar of international businesses that are looking to expand. Diamond Recruitment has been at the forefront of the local recruitment sector for many years and I'm sure it will remain a key player in the market as part of Staffline."
He said Carson McDowell had now worked on more than 20 mergers and acquisitions (M&A) in 2015, which was up substantially on 2014.
"This reflects the mood of quiet confidence that is slowly permeating the business community and we expect the level of M&A activity to increase, both among large companies and SMEs, in the year ahead."
Ms McKenzie is also a former operations director at recruitment firm Ranstad.
She resigned from N121 - a political party started up by former Ulster Unionists John McCallister and Basil McCrea in 2013 - on the night of the European elections last year.
The party imploded after unproven allegations of misconduct against Mr McCrea.