The company revealed that the proposed acquisition of Engine by Lake Capital had been "comprehensively approved" by shareholders and was expected to complete "very shortly".
The deal was delayed by a group of around 50 ex-employees who were unhappy that the terms meant they would have to sell their shares in the business and accept a lower value per share than current employees.
Engine needed 75 per cent of shareholders to accept its offer for the deal to go through.
It is not clear whether Lake sweetened the deal or whether the rebel shareholders caved in.
Peter Scott, chief executive of Engine Group, said: "This is the beginning of the next stage of the Engine growth story, the first ten years having been spent building an intrinsically different model that we believe we can expand both organically and through acquisition, particularly in the US and Asia."
A partnership between Engine and Lake’s current investments, which include the market research company ORC International and the content management agency Trailer Park, will be launched soon.
The enlarged Engine Group will use Lake’s operational and financial backing to take advantage of "growth opportunities" as the world economy begins to recover.
Terry Graunke, co-founder of Lake Capital, said: "We believe that the combined Engine, ORC and Trailer Park business will form the basis of a major, independent global force in marketing services and communications. We are very excited about working together with such great agencies, people and clients."