It becomes Four's second agency acquisition, following Broadgate Mainland, since it secured a £10m investment from the Business Growth Fund (BGF) earlier this year.
FBA, which has an annual fee income in excess of £1m, already works with Four in a consortium called Four Cymru, and this will be the trading name in the future for all work in Wales.
FBA has a staff of 16 will continue to be led by MD Meilyr Ceredig, who joins Four’s practice board. Founder and chair Sue Balsom will continue to be a consultant to the agency.
FBA’s client list includes Welsh Government contracts for food promotion, tourism, education, health and social behaviour programmes. Other clients include Higher Education Wales, Ceredigion Council, Food Innovation Wales, Lantra, Christian Aid, Rachel’s Organic, Visit Wales and Fork2Fork. The agency also created and manages the annual Welsh Politician of the Year awards with ITV Wales and provides pro bono support to the Cambrian Mountains Farmers Initiative.
Four said FBA’s in-depth understanding of Wales would complement its property, financial services, public sector, sports, travel and transport teams.
Four Communications CEO Nan Williams said: "The energy, heritage and passion of FBA makes it one of the most impressive independent consultancies in Wales today. We are proud that it will become part of our Four family and thrilled to welcome the exceptional leaders of FBA management to our senior management team.
"Born and brought up in Wales, I am also particularly pleased to be able to invest in Wales and see major opportunities ahead for the Welsh creative economy."
Ceredig said: "We wanted to merge with Four because the people there have the same commitment to their clients and their people as we have at FBA. It also means that we can offer clients in Wales a wider UK and international reach with more sector specialisms.
"As Four Cymru, we will be able to provide both staff and clients with a much broader, deeper service. As part of an integrated, but still independent, group we can now offer more and new services like digital, advertising and media buying."
Earlier this year Four also bought healthcare media planning and buying agency MSA Media. Previous acquisitions have included Consolidated PR, Colman Getty, bgb and Kinross+Render.
Speaking to PRWeek in August following the BGF investment, Williams said she was planning a "raft of acquisitions". Four planned a move into healthcare PR and expansion further overseas to South East Asia in particular, she said.
As part of the investment, Four also secured an additional debt facility from HSBC.
Four has a total fee income of about £20m, employing more than 250 staff.