It was composed specifically for the purpose of allowing the bricklayer roadies more time to finish constructing the wall, to seal off the stage almost completely, before Waters appeared in the last one-brick-wide space in the wall to sing "Goodbye Cruel World", and end the first part of the show.
The piece doesn't have a strict composition, varying from venue to venue, but it usually contained themes from "The Happiest Days of Our Lives", "Don't Leave Me Now", "Young Lust", "Empty Spaces", and occasionally, when the bricklayers were running especially late, a jam (in the jazzier style of the earlier, improv-oriented Floyd) similar to "Any Colour You Like" (D minor to G major), was played.
The themes from "Don't Leave Me Now" and "Young Lust" were transposed down a whole step, so, like much of the album, "The Last Few Bricks" is in D minor—which leads to a "brightening" effect, when "Goodbye Cruel World" begins in the parallel key of D major.
During the mixing and editing of this album, producer James Guthrie suggested the title "The Last Few Bricks" for the bridge.
The longest performance of this medley was on 7 February 1980 at Los Angeles Sports Arena when "Another Brick in the Wall (Part III)" was stretched to over 13 minutes.