The lingerie tycoon took to Twitter and Instagram to reveal that billionaire Doug Barrowman - who she started dating in 2016 - has proposed.
Michelle, 47, posted a picture of them together with the caption "I said yes".
Michelle - who founded underwear brand Ultimo - and Doug, 53, have been inseparable since they started dating two years ago and Michelle previously called their romance a "fairytale".
She said: "My mum told me, 'You won't find love if you're looking for it', and honestly, it was the last thing I was looking for."
But as you get older, you realise what you want from a relationship and I couldn't deny there was a true connection. I feel like I'm in a fairytale, a beautiful dream I don't ever want to wake up from.
"In every way, I came to see that I'd met my match in this amazing man and no one has ever made me feel as cherished or respected.
"Everything about our life together feels so natural, we have fun and laugh so much, we have the same outlook and drive. Even our kids could see it was meant to be."
Michelle - who is known as Baroness Mone of Mayfair - and Doug, met at a business dinner and currently live together on the Isle of Man.
He is believed to own more than 50 businesses, a private jet and six homes.
Michelle split from her first husband Michael in 2011.