The newly-married actress, 28, will play an army medic in war-torn East Africa.
As revealed in the Sunday People (21 June), she will take over from Lacey Turner in the drama.
It will be Michelle's first leading role since she left Coronation Street last year.
According to the newspaper, Michelle agreed a £250,000 deal after returning from honeymoon with husband Mark Wright.
The first series followed medic Molly Dawes in Afghanistan, but Lacey Turner has since returned to EastEnders.
Michelle will play Corporal Georgie Lane on a dangerous mission in Kenya.
She said: "I'm a massive fan of the series so I can't wait to be a part of it. It's going to be a big but exciting challenge for me."
A BBC spokesman told the Sunday People: "It won't be an easy posting as she has to earn the love and trust of her fellow soldiers, and the greater respect of her commanding officer, while working alongside aid workers in the world's biggest refugee camp."
"Kenya will be full of surprises that will challenge Georgie professionally and personally."
Filming abroad on the second series of Our Girl starts in January, and it will be screened in late 2016.
We last saw Michelle as part of an ensemble cast in Ordinary Lies.
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