The former England international also turned out for LA Galaxy, AC Milan and Paris Saint-Germain in his career.
To honour the occasion he posted a picture of himself on Instagram from that day alongside Real legend Alfredo Di Stefano, holding up the now famous number 23 shirt.
Beckham also included a message with the picture, saying: "This day 12 years ago I moved from the mighty Manchester United to the mighty of Real Madrid. Huge honor to have played with 2 of the biggest clubs in the world. Great memories."
His move to Spain was a massive high profile switch, and one that signified a swelling of the Beckham phenomenon that would arguably go on to define the England star, certainly on a global scale.
Though there it is hard to deny that the now 40-year-old was an outstanding footballer for his country, and each of the clubs he turned out for in his career, the method with which the player and his sides benefitted from the media coverage surrounding Beckham was something football had never seen until his appearance.
Beckham was reluctant to leave Manchester United, after six Premier Leagues, two FA Cups and a Champions League triumph, but at Real he became one of the Galacticos, the only English one that did so with some success. The midfielder won the La Liga in his final season, before heading off to LA Galaxy to help move the football spotlight onto a whole new country.