A palace source said the Duchess is "honoured and looking forward to continuing to work on behalf of Her Majesty going forward".
Awards under the Royal Victorian Order are made personally by the Queen, without advice from government, for services to the sovereign. The RVO has five classes from member to Knight or Dame Grand Cross, its highest honour, and was founded in April 1896 by Queen Victoria as a way of rewarding personal service.
Eighth wedding anniversaries are traditionally marked with gifts of bronze.
Earlier today, Kensington Palace thanked royal fans for their well wishes as they reminisced over social media photographs of Prince William and Kate Middleton on their wedding day on April 29, 2011.
The Cambridges, who just last week celebrated Louis' first birthday, are getting ready for Charlotte's fourth birthday on Thursday.
The pair, who now have three children - Prince George, Princess Charlotte and Prince Louis - were flatmates after meeting at St Andrews university in Fife, Scotland.
They dated for more than eight years before finally marrying in the grand surrounds of Westminster Abbey in central London in front of 1,900 guests, watched by a global television audience of millions.