Enterprise AI adoption is increasingly constrained by the difficulty of integrating AI capabilities with legacy platforms that continue to support critical business operations. Mainframe environments, SAP deployments, and proprietary enterprise applications contain established business logic, transactional data, and operational knowledge, but often lack standardized interfaces for direct interaction with modern AI systems. This article develops an Enterprise Copilot Architecture for Legacy Systems that enables AI copilot services to interact with legacy applications without requiring their replacement. The proposed architecture introduces an Intelligence Integration Layer that combines layered integration, service-oriented and API-driven communication, event-driven processing, agent-based intelligence, human-in-the-loop governance, and security-by-design. The approach further incorporates hybrid processing separation, multi-layer caching, context-aware retrieval, containerized deployment, and adaptive compute scaling to reduce processing overhead and minimize disruption to legacy platforms. The architectural analysis indicates that the proposed mechanisms provide a structured pathway to connect AI services to heterogeneous legacy environments while maintaining controlled access to enterprise data and business functions. The architecture also supports separating AI processing from core transactional workloads, allowing computational demands to be managed without directly modifying legacy applications. Context-aware retrieval facilitates access to institutional knowledge embedded in legacy systems, while governance mechanisms maintain human oversight over AI-generated actions and recommendations. The resulting framework demonstrates how contemporary AI capabilities can be introduced incrementally into established enterprise environments while preserving existing business logic, operational continuity, security controls, and architectural sustainability. It therefore provides a non-invasive architectural approach for extending legacy enterprise systems with scalable and governable AI copilot capabilities