The 64-year-old star - who attended the nuptials at Windsor Castle last month - believe the pair's union was on a "whole another level".
She shared: "I was unprepared for the depth of emotion I felt stepping onto the grounds of Windsor Castle. It literally took my breath away. I exclaimed out loud to no one in particular: 'Whoa! This right here is a whole another level! And I thought immediately of the history, the legacy, the astounding moment Meghan Markle was stepping into.
"And what it would take to be prepared for such a moment. The life she was leaving behind and the new world to which she was rising - all part of a destiny she helped design. It gave us hope, that wedding. Hope that we can all do what Mara Gay described in her New York Times opinion piece as 'imagining the day when we wake up and remember who we want to be.'"
And Oprah loved how the duo were "glowing with happiness".
Writing in the August issue of O, The Oprah Magazine, she added: "We all want to feel as radiant, joyful, and alive as Meghan looked on her way down the aisle to meet Harry. Both of them were glowing with happiness. I can't wait to see the goodness that will come from their union. Goodness that I know for sure will help change the way the world thinks about what is possible, even more than it already has."