While on tour in the UK and Ireland, both Barack and his Vice President Joe Biden warned voters of the consequences a Britain outside of the EU could have – particularly its relationship with the US.
But three years after the Leave campaign succeeded, Michelle told those who were frustrated at the outcome of the vote to make their opposition heard.
It came during an event in London to promote her book, where she admitted the UK was experiencing the same “anxiety” with politics that was then facing the US.
At the time, Donald Trump had secured an unlikely US election win, and was into his second year in the White House.
Michelle told the audience that the world had “changed before” and that despite having “some tough times on this planet… we’ve come out of it”.
She added: “It is time for us to roll up our sleeves.
“And if we are not happy with the state of things, then in democracies we have votes.
“But that means you’ve got to pay attention and we have to be engaged and we can’t take our rights and liberties for granted, because if we don’t vote, somebody will and that means that’s the direction of the country that we’re in.
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He added: “Had I been a Member of Parliament, had I been a British citizen, I would have voted against leaving.
“From the US perspective, US interests are diminished with Great Britain not being an integral part of Europe and being able to bring influence.
“There’s growing awareness that Britain played a role in Europe the last 30 years that went well beyond the notion of open borders and trade, being able to influence attitudes.”
It emerged after Barack’s intervention two months before the vote that he was asked by Mr Cameron to issue the exact warning he delivered, according to reports.
Ben Rhodes, an ex-White House adviser, admitted Mr Obama’s dramatic intervention was specially requested by Mr Cameron.
He told BBC Radio 4’s Today programme in 2018: “We had come here to try to help the Remain campaign and we had a meeting with David Cameron and his team.
“We were all in violent agreement about the negative consequences of Brexit.”
Mr White noted that some of the arguments for the UK to leave emphasised how Britain “could just negotiate its own free trade deal agreement quickly”.
He added: “As Obama was saying that, somebody on the British side said ‘yes, we’d end up being back of the queue’ and everyone laughed and Obama said ‘that’s exactly right’.
“Then he was asked ‘well, it would be good if you could repeat that point in the press conference’ and, of course, he did.”