Video report by ITV News Correspondent Lucy Watson
Meghan, 38, attended the opening ceremony of the One Young World Summit at the Royal Albert Hall in London.
The four-day event, described as a “global forum for young leaders”, brings together 2,000 young people from more than 190 countries.
She wore a long purple dress for the event, during which she was described as a “global champion for the rights of women and girls”.
Meghan arriving at the event
She was sat next to Nobel Peace Prize recipient Professor Muhammad Yunus for the event.
Meghan said she tried to cope with the pressures of her new life since marrying the Duke of Sussex in May 2018 by putting on a “stiff upper lip”.
But she said she was not prepared for the intensity of the tabloid interest.
London mayor Sadiq Khan, actor Warwick Davies and One Young World co-founders Kate Robertson and Dave Jones were among the speakers during the summit opening.
Mr Khan said: “When it comes to tackling the defining challenges of our time, we achieve more together than we do alone.
“This is the main message I want to send to you this evening. Shamefully there are some politicians who wish to absolve themselves from their positions of responsibility.”
According to the One Young World website, Meghan is a “long-standing supporter” of the organisation, having joined as a counsellor at the 2014 summit in Dublin.
The source said Harry and Meghan had “single-handedly modernised the monarchy” and added the couple were surrounded by people “afraid of and inexperienced” at how best to “deploy their value”.
The source told the BBC there was a view from The Queen and other senior royals that the couple were “in a fragile place”.