This study reports the development of heavy-section hollow rectangular forgings of aluminum alloy AA2219 in T852 temper with a ruling section thickness of 360 mm and establishes the associated processing–microstructure–property relationships. Traditional solid forgings of this size often suffer from quench sensitivity, where the slow cooling of the inner core leads to inconsistent mechanical properties. Unlike conventional solid thick-section forgings, the present work introduces a premachining-assisted hollow configuration prior to heat treatment to mitigate quench sensitivity and improve through-thickness property uniformity. An optimized open-die forging route was designed to control material flow, strain distribution, and thermal history during processing. Detailed microstructural characterization reveals uniform grain flow patterns and refined microstructural features across the section, which directly contribute to the enhanced mechanical performance. The results demonstrate that this hollow-core approach ensures total ultrasonic integrity and meets strict aerospace standards for mechanical performance, providing a scalable solution for manufacturing large-scale structural components.