The deal will result in DP&A working alongside Banks Hoggins O'Shea/FCB to augment FCB's integrated offering in London.
It will also act as a catalyst to drive the business of FCBi, the group's DM European network, in the key markets of France, Germany, Spain and Italy.
The possible acquisition of DP&A was first mooted three years ago - when FCB had no DM resource - and its completion is a significant step in its evolution as a fully integrated communications provider.
DP&A, with 70 staff and a client list which includes Goldfish, BSkyB and Air Canada, will retain its name and management. Dave Poole, the DP&A chairman, will also head FCBi in Europe.
Harry Reid, FCB's European president, said: "It has always been our intention to create and secure the strongest brands and offerings in both the advertising and DM arenas in the UK.
"Bringing DP&A into the FCB fold fits this bill, and the agency's impressive credentials will strengthen the group's European offering."
Poole claimed DP&A had shunned a number of offers from other networks before agreeing to join the Interpublic stable.
"You can only go so far as a domestic business, and over the course of the past 18 months it became clear that FCB has a real understanding of the way the industry is going, and of the need for a strong direct marketing product, he said.