To be called InterbrewAmbev, the combined group will have sales of 9.5bn euros and have14% of global market share. The new company expects synergies of 280m euros.
Interbrew said: "Operating with one unified vision, each unit will maintain its focus, while at the same time sharing best practices, capturing synergies and avoiding any duplication of resources where possible."
The new company said that it expects to be at number one or number two in more than 20 beer markets.
Interbrew chief executive John Brock will become chief executive of the new company and Interbrew’s chairman Pierre Everaert will chair the new group.
Brock said: “Joining with AmBev, Latin America's leading brewer, and its world class management team, is great news for our consumers, employees, distributors and shareholders.”
Belgian-based Interbrew will issue 141.7 million new shares to Braco - the holding company of AmBev - to give Interbrew control of Braco and a 21.8% economic interest in AmBev.
Interbrew said it would take 9.5 billion ordinary shares in AmBev and 13.8 billion preferred shares, while AmBev will take Interbrew's 70% interest in Labatt USA and 30% stake in Femsa Cerveza.
This second part of the deal will see Interbrew assume $1.5bn of debt from AmBev.
InterbrewAmBev will be headquartered in Belgium, while AmBev will be headquartered in Sao Paolo.