At the Victoria and Albert Museum, Gareth Williams specialised in the history of furniture design since 1800, and worked on gallery displays devoted to Frank Lloyd Wright and Twentieth-Century Design. Increasingly drawn towards contemporary design, he curated displays about young designers including Inflate and Matali Crasset. With Jane Pavitt he curated Brand.New (2000), an exploration of brands and branded culture, and in the same year (with Sorrel Hershberg) he curated Ron Arad, Before and After Now, the first large exhibition of work by the designer in a major UK museum.

The representation and interpretation of contemporary design in the museum setting has been Williams' focus of interest for several projects, most notably Milan in a Van (2002), an ‘instant exhibition’ of works premiered at the Milan furniture fair and displayed at the V&A only a week later.

In 2004 Williams was the Project Curator for the Architecture Gallery, a major permanent display of architectural fragments, models and drawings from the V&A and the RIBA Drawings Collection, covering 3,000 years of world architecture.

Gareth Williams' first major book, The Furniture Machine: Furniture since 1990 (2006), examined innovative design of the period and the creation of an expanded market for contemporary design, particularly in Britain. This was followed by the exhibition and book Telling Tales: Fantasy and Fear in Contemporary Design (2009), Williams’ final exhibition at the V&A. The project, which focused on one-off and limited edition works by designers, which shared a similar narrative character and are often traded through the gallery system, became a landmark of the so-called ‘Design Art’ debate in the late 2000s. Gareth Williams joined the RCA Design Products department in January 2009.

Gareth Williams has contributed to many books and magazines, lectured widely, in New York, Moscow and elsewhere, and served on many design prize juries. Until 2010 he was one of the longest-serving members of the selection panel for 100% Design, and has also selected for Salon Satellite in Milan.