The buyer, inter-Arab development bank Arab Petroleum Investments Corp., will see its overall ownership in the joint venture rise to 17 per cent.
Methanex says its will remain the operator and majority shareholder with just over 50 per cent of the company's equity.
The remaining 33 per cent interest in EMethanex is held by several Egyptian government shareholders.
The deal is expected to be completed by the end of the year.
Vancouver-based Methanex is the world's largest supplier of methanol to major international markets.