The 33-year old moves to the subcontinent after his contract with Turkish Super Lig side Kayserispor expired on July 1.
This is the 10th club he will be representing in his professional career, having had stints in home country Ghana with Liberty Professionals, as well as Italy, England, France, United Arab Emirates, China and Turkey.
"I am extremely excited to start this new chapter in my career," Gyan told the media.
"I have heard great things about NorthEast United FC and the Indian Super League and I am thrilled to be a part of it for the upcoming season.