The firm, formed this week, will have 20 staff, largely from BDP. It will be headed by BDP's Roy Adams, who will be chairman, and PCM boss Chris Paxford, who will be managing director. Colin Dunne, formerly at Wates, will be operations director.
Adams said what the firm was offering was unparalleled.
He said: "The knowledge bases of our two companies are unique, and we know that by using our joint resources we can satisfy the needs of our clients."
Paxford said the two firms had transferred existing work into the joint venture. He said it was already bidding for work, including an office refit, and that the joint venture aimed for a turnover of £10m in its first five years.