"You're just as mobilised and energised to see the change we all need and deserve. This fight is worth fighting and we all need to be out there mobilising to have our voices heard.
"If you aren't part of the solution, you're part of the problem. If you are complacent, you are complicit."
She added: "This fight is worth fighting and we all have to be out there mobilising to have our voices heard.
"We can make a difference in this election and we will make a difference in this election."
Her comments were met by fierce criticism from Morgan, who accused her of breaching royal protocol. Traditionally royals are not advised to share political opinions publicly.
Taking to Twitter, Morgan urged the Queen to remove Harry and Meghan's titles.
The Good Morning Britain host wrote: "The Queen must strip the Sussexes of their titles. They can't remain as royals and spout off about foreign elections in such a brazenly partisan way."
He added: "Last time I checked she's still calling herself the Duchess of Sussex."
Harry and Meghan stepped down as senior royals earlier this year – though they still hold the titles of the Duke and Duchess of Sussex.
It's not the first time Meghan has had strong words for the US President.
Meghan detailed why she didn't like Trump in a 2016 interview on US talk show.
She said: "It's really the moment I go. We film Suits in Toronto and I might just stay in Canada.
"Yes, of course, Trump is divisive, think about female voters alone, right?"