The building, parts of which are listed, was designed by the architect Joseph Diongre [fr] and completed in 1938 in Streamline Moderne, an international style of Art Deco.

[3] The building owes its name to Eugène Flagey, a Belgian lawyer and politician[4] who served as mayor of Ixelles from 1935 to 1953.

[8] The building garnered critical acclaim as soon as it was finished, and the qualities of the studios attracted renowned classical, contemporary and jazz musicians to perform there (including Chuck Berry, Jerry Lee Lewis and Chet Baker[2]), for live concerts and recordings.

[9] The INR/NIR was later split into separate broadcasting entities, one for each language,[9] the Dutch-language VRT and the French-speaking RTBF, before they moved out of the building completely in 1974 (after growing out of it[6]) and leased it to various other cultural bodies until the late 1990s.

[11][12] As a non-profit organisation Le Flagey has the following aims: The central portion of the building is dedicated to cultural activities, with five recording studios that are flexible in size and function.

[14] The original design incorporated twelve recording studios, which were built in two acoustic towers forming the core of the building.

[8] The 2002 renovation restored the Flagey Building's original functions by creating a musical space with recording studios and concerts venues, allowing it to host an eclectic programme of events.

[16][6] The whole back wall is occupied by an organ, specially designed for this space and built by the Tournai organ-builder Maurice Delmotte.