The Norfolk and Norwich Millennium Library sits to the west end of the building, with office and commercial spaces and studios for the BBC around a main atrium.

The library has been named one of the most popular in the country, while The Forum is a venue for public events and festivals and the outside plain hosts live performances.

The structure consists of a three-storey concrete frame with a surrounding brick wall, with the brickwork made to emulate that of the adjacent City Hall.

[21] The American library was dedicated on 6 November and the ceremony, which was attended by 2nd Air Division veterans, included a service from the Bishop of Norwich and a 28-piece orchestra.

[19] As part of her tour celebrating her Golden Jubilee, Queen Elizabeth II visited Norfolk on 18 July 2002 and officially opened The Forum.

[31] The area in front of the building, known as Millennium Plain, is used for public events, performances, live music, festivals and exhibitions.

[34] Queen Elizabeth II also praised the building during the opening ceremony, while RIBA described it as an "architectural tour de force and major contribution to urban cultural and social life in Norwich.

"[22][25] Jonathan Glancey, who visited The Forum four weeks after its opening, described it as a "heroic if ultimately flawed attempt to create a dignified public meeting place to satisfy complex and contradictory needs and desires".

[35] He described it as resembling an airport terminal and suggested that the library should be housed separately to the commercial area of the building, pointing out the Pizza Express as an example.

[35] Giles Worsley, writing for The Daily Telegraph, said that[18] [s]ometimes Hopkin's combination of very different materials can lead to unexpected results.

The mixture of heavy concrete beams, glass, steel and laminated wood struts in the central hall of Portcullis House... may have driven more purist Modernists into a frenzy of agitation but it is a bold and memorable space in stature with time.

Although shopping malls are an increasingly dominant building type, it seems sad that with more than £63 million to play with, an architect of Hopkin's skill could not have come up with something more distinctive.