The two will each own 50 per cent of the business, which will become one of the country's biggest plants for drying, cleaning and grading cocoa beans.
Cameroon's cocoa has a particular taste and is used only by a small number of processors such as Cargill, ADM and Barry Callebaut.
However most cocoa plants in the country are small.
"In Cameroon it is difficult to set up processing for economy of scale," an Olam spokesman told AP-Foodtechnology.com.
"This deal will allow us to scale our volumes in Cameroon and increase our business in Cameroon cocoa," he said.
"Our strategy in cocoa is to have a dominant position in every market worldwide."
Less than 20 per cent of Olam's cocoa customers are based in Asia, with most from the US and Europe.
ADM is one of the firm's key customers.
The partners plan to further upgrade the Usicam plant for processing cocoa beans.
Usicam, previously owned by French group SAGA, has in turn acquired the cocoa processing assets of SDV in Cameroon.
Olam said in a statement that the partners will "ensure that cost economies and usinage efficiencies may be offered to the cocoa suppliers in the country before they export the beans" .
The industry is under pressure to support a sustainable cocoa sector with consumers increasingly turning to fair trade products that guarantee better prices for cocoa farmers.
Cameroon produced 160,000 metric tonnes of cocoa in the latest season, down on the previous year due to erratic weather and floods in the main producing areas.