One of the biggest obstacles in the wide-spread industrial take-up of Grid technology is the existence of a large amount of legacy code that is not accessible as Grid services. The paper describes a new approach (GEMLCA: Grid Execution Management for Legacy Code Architecture) to deploy legacy codes as Grid services without modifying the original code. Moreover, we show a workflow execution oriented Grid portal technology (P-GRADE portal) by which such legacy code based Grid services can be applied in complex business processes. GEMLCA has been implemented as GT-3 services but can be easily ported into the new WSRF Grid standards.