This is the first official signing since the BCCI cleared the women cricketers to participate in overseas leagues earlier this month.
On the final day of the Indian board's working committee meeting in Dharamsala today, the BCCI president Anurag Thakur confirmed that Harmanpreet has been signed by the Thunder.
Harmanpreet, India's vice-captain, had received offer from three teams, including the Sydney Sixers, the runners-up in the inaugural season but she zeroed in on the Thunder.
"We have a pretty solid team... But we have an opportunity to bring another overseas players in and we'll be looking to spend that spot wisely. Hopefully we'll get one of the best players around the world."
India women's team had recorded their first-ever bilateral series win in Australia, winning the T20 series 2-1 ahead of the World T20, and Harmanpreet contributed a 31-ball 46 in a historic chase in the series opener.