ATPI, which has clients from the oil and gas sectors, will use Abreu for regional on-the-ground assistance in Angola, Spain and Portugal.
ATPI Group chief executive Graham Ramsey said: "Expanding our international network is an ongoing commitment of ATPI in order to service our client base.
"Spain and Portugal are both areas of great growth and Angola, which can be a complex region to work, will deliver trusted support to our existing customers and new partners who work within the region."
Abreu Travel Group managing director Paulo Ribeiro added: "With a firmly established business in Portugal, Spain and Angola, we’re proud of our specialism in these countries. Becoming a new a partner to ATPI Group means that we can offer these professional skills to the international clients of ATPI."
ATPI Group now operates a network of 49 offices in 27 countries.