A 50-foot model of the game's Glyph symbol was flown over the River Thames by helicopter, from Greenwich Peninsula to Tower Bridge, backed by dynamic effects.
More than 500 Halo fans turned out to watch the show, which featured one of the largest and brightest man-made structures to ever fly over a capital city.
"Halo launches are renowned for being entertainment game-changers and we are back with our most ambitious projects to date," said Microsoft executive Chris Lewis.
"Last week we created a replica of the Halo universe within the heart of Europe. This week we have one of the world's largest and brightest performance art objects being flown over London.
"The Glyph flyover makes the seemingly impossible world of science fiction a reality, a 50-foot symbol of the Didact hovering in the skies of a major capital city, seems a fitting way to herald the next chapter of this phenomenal blockbuster franchise."
Celebrities including JLS, The Wanted and Made in Chelsea stars gathered to watch the Glyph, while fans and spectators were treated to an epic aeronautical show.
Following the dramatic display, the official flagship London midnight launch took place at GAME in Westfield Stratford, where fans queued for hours to get their hands on the game as it was released earlier this morning (November 6).
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Watch a trailer for Halo 4 below: