BDP beat three rival practices to secure the interdisciplinary contract for client advisory services to help ensure the safe and secure future of the palace.
The appointment covers landscape architecture as well as architecture, civil and structural engineering, building services engineering, interior design, lighting design acoustics and planning.
Grassed areas and other landscapes weave between neo-gothic buildings. They include a tree-lined area beside the Thames and the palace garden, once a place to grow fruits, flowers and fresh herbs.
Since its construction in the 1800s, many features and systems in the palace have never been renovated, and the heating, ventilation, water, drainage and electrical systems are antiquated.
BDP director Tim Leach said: "This new programme of work presents the unique and very special challenge of responding to the needs of parliament and its visitors, and conserving its historic fabric for this and all future generations."