The royal couple were joined by Roy Hodgson and his England team to tour the complex built by Bowmer & Kirkland.
The new training centre will be home for all 24 England teams and a base to raise the profile of English coaching.
The full England squad will train there for the first time ahead of their 2014 World Cup qualification game against San Marino on Friday.
Julie Harrington, Managing Director of St.George’s Park, said: “I’m thrilled and really proud that they are coming to have a look at what is the culmination of a lot of hard work by a huge number of people.”