India had earlier defeated Derbyshire by seven wickets. After Harshal Patel lifted India from a precarious position to 149 for eight with a 36-ball 54, the visiting bowlers fired in unison to bowl out the county side for 139 with three balls to spare.
Arshdeep Singh, Avesh Khan, Yuzvendra Chahal and Harshal picked up two wickets apiece as Northamptonshire failed to overcome India's total.
Earlier, asked to bat first, India were off to a disastrous start losing Sanju Samson in the very first delivery of the match, the successful bowler being skipper Joshua Cobb.
One-down bat Rahul Tripathi, too, did not last long but more trouble awaited India as pacer Brandon Glover sent back Suryakumar Yadav to leave the visitors tottering at 8/3 in the third over.