The Duchess of Sussex has told young leaders from around the world "you are the future, you are the present" in her first UK speech since stepping back as a senior royal.
The Sussexes' attendance at the ceremony was their first UK public appearance since the Queen's Platinum Jubilee in June.
Meghan told young leaders from more than 190 countries: "You are the ones driving the positive and necessary change across the globe now, in this very moment.
"And for that I am so grateful to be in your company today."
She also told those gathered: "You are the future... you are also the present."
Meghan also spoke about having a "pinch me moment" after the first time she was asked to be a counsellor for One Young World in 2014.
She said: "And there I was, the girl from Suits. I was surrounded by world leaders, humanitarians, prime ministers and activists that I had such a deep and long-standing respect and admiration for.
"And I was allowed in, to pull up a seat at the table.
"I was so overwhelmed by this experience, I think, I think I even saved my little paper place-marker with my name on it.
"Just proof - proof that I was there, proof that I belonged, because the truth was, I wasn't sure that I belonged.
"I was so nervous, I doubted myself and I wondered, wondered if I was good enough to be there?"
But she added One Young World, "saw in me, just as I see in you, the present and the future".
'This is where it is all beginning'
Meghan told the 2,000 or so delegates listening to her speech: "I want to make that point because often times I speak to young adults about the years ahead.
"About what you will do, about what you will have to adopt to fix from previous generations and also what legacy you will leave.
"Too often in that, we neglect the point - you are doing it now.
"You, here, in this present moment, this is where it is all beginning."
Before the duchess' speech, Harry and Meghan were sat centre stage on a bench together as they watched bearers carry the flags of more than 200 countries.
Sussexes travel to Manchester by train
Meghan sat with her legs crossed and swayed in time to a rendition of Dancing In The Streets as she clapped her hands.
Reports suggest Harry and Meghan arrived in Britain on Saturday, but a spokeswoman for the couple declined to confirm their arrival.
The couple were pictured walking into a side entrance of London Euston station on Monday as they took the train up to Manchester for the summit.
They were reportedly driven the 27 miles from their UK base at Frogmore Cottage in Windsor to Euston in a hybrid electric Range Rover.
Meghan says her race become an issue after she met Harry
Their UK trip comes just days after Meghan's wide-ranging interview with The Cut magazine, in which she said she had "really made an active effort to forgive" both her in-laws and members of her own family after stepping back from royal duties.
She added that she is "still healing" from the ordeal.
The former Suits actress also said that "just by existing" she and Harry were "upsetting the dynamic of the hierarchy" before they stepped down as senior working royals.
Meanwhile, in the latest episode of her Archetypes podcast, Meghan said her life only became more focused on her race after she started dating Prince Harry.