The London studio – led by architects Alex de Rijke, Philip Marsh and Sadie Morgan – wins the biggest prize in UK architecture for transforming a century-old, ruined pier into a new attraction for the seaside town.
RIBA president and jury chair Ben Derbyshire described the project as a "masterpiece of regeneration and inspiration".
"Hastings Pier showcases the remarkable skills, tenacity and problem-solving flair of its talented architects, dRMM," he said. "The architects and local community have transformed a neglected wreck into a stunning, flexible new pier to delight and inspire visitors and local people."
Hastings Pier was first constructed in 1872. It enjoyed great success in the 1930s, but became neglected in recent decades, and was permanently closed in 2008. Two years later, it was ravaged by a devastating fire.
The architects were tasked with repairing the structure, and making it suitable for a wide range of activities. To do this, they rejected the typical pier format – a deck covered with commercial booths – and instead opted for a more open space.
Their redesign is completed by a visitor centre clad in salvaged wooden boards and a grand external staircase that doubles as a performance space.
The Stirling Prize judges – who included Indian architect Anupama Kundoo, Caruso St John Architects co-director Peter St John and Assemble co-founder Jane Hall – said the project "evolved the idea of what architecture is and what architects should do".
"dRMM's role has been utterly pivotal in realising this masterpiece of subtle, effortless design," they said.
"They have driven this project through to completion: campaigning, galvanising and organising local support throughout each aspect of the funding stage. They went above and beyond what most people think of as the role of the architect – and then they kept going!" they continued.
"Councils across the country should take inspiration from Hastings Pier, and open their eyes to the unique assets that can be created when such collaborations take place."
The Stirling Prize is awarded annually to the project judged to have made the biggest contribution to British architecture in the past year.
Hasting Pier was selected ahead of five other shortlisted projects: Barrett's Grove by Groupwork and Amin Taha; British Museum World Conservation and Exhibitions Centre by Rogers Stirk Harbour + Partners; Command of the Oceans by Baynes and Mitchell Architects; City of Glasgow College City Campus by Reiach & Hall Architects and Michael Laird Architects; and Photography Studio for Juergen Teller by 6a Architects.
It marks the first time dRMM has won the prize, although the studio has been shortlisted twice before – for Clapham Manor Primary School in 2010, and for the Trafalgar Place housing development in 2016.
Studio co-founder Alex de Rijke said his team were "proud of achieving the apparently impossible" with the project.
"This space offered more potential than an 'iconic' building on the end of the pier, and demonstrates the evolving role of the architect as an agent for change," he said.
Last year's winner was Newport Street Gallery, which Caruso St John designed for artist Damien Hirst.
Photography is by Alex de Rijke, unless otherwise indicated.