The new entity - called SEC Newgate - is targeting acquisitions, with "one or two" expected by the end of the year, CEO Fiorenzo Tagliabue has told PRWeek.
SEC Newgate - which debuted on London's secondary market, AIM, this morning - will comprise around 600 people working from 30 offices in 14 countries and across
four continents. Combined turnover of Porta and SEC in 2018 was $79.1m (£65m).
The new group's PR agencies include Porta shops Newgate, Publicasity and Engage Comms, alongside several SEC consultancies such as London-based public affairs specialist Newington.
There had been a question about whether the merger would lead to agencies being consolidated.
Newgate CEO Emma Kane told PRWeek: "Going forward, all the future cross-border client projects are going to use the SEC Newgate brand. The domestic projects will continue to be delivered under the local agency brands.
"The business has acquired and built very strong local brands. In fact, one of the key strengths that we see that we have is the local/national/international positioning."
Kane said it was "business as usual" for the brands, but she spoke of the opportunity to "enhance the offering and work together" with a "seamless integrated service across the spectrum of communications offerings".
London-based Porta and SEC, which was headquartered in Italy and floated on AIM in London in 2016, have been working together on projects since the latter acquired a 19.3 per cent stake in the Newgate owner in August 2017.
Kane gave the example of current services being expanded across the group: its research offer, which started in Australia and launched in the UK this year; and the public affairs offering, which "will be leveraged more widely across the SEC Newgate group".
"We've got the opportunity now and the scale to be a really significant and cohesive communications group across a much bigger footprint, and a strong balance sheet," Kane said.
"It's a very unusual situation to get two international groups come together where there's no crossover in the footprint."
Services offered across the new group include public affairs and advocacy, financial and corporate comms, digital insights, research, crisis management and consumer PR.
Tagliabue said the new company is "going to see if there are the possibilities of savings, which is normal".
Asked about redundancies, Kane said there would be "no significant changes on that front", adding: "This is about building the group; this is not about losing lots of people."
As PRWeek reports today, Neil Kleiner, managing partner and strategic head of digital at Newgate and Publicasity, has left the business to join Way to Blue as UK MD. Kane said this was unconnected to the merger.
Asked about acquisitions, Tagliabue said the first priority is organic growth, but the company has "a plan of acquisitions".
"We are working at the moment in about three or four countries - we can not give the details. We think we will make one or two acquisitions by the end of the year."
Asked if these were PR agencies, he said: "Yes. Above all we are working on countries where we are not present in order to increase our geographical worldwide footprint."
The statement announcing the agreement to merge in June valued Porta at around £4.5m. Kane said the figure is "completely misleading" because it doesn't take into account debt obligations.
Tagliabue said: "The experience of SEC is over. The experince of Porta is over. There's a new player on the market as the group brand SEC Newgate, with, of course, the domestic brands of the different companies, which are part of this new entity."