The coveted 22-year-old attacker has chosen to move back to his hometown club at the end of the season on a deal lasting until the summer of 2017, his current side confirmed
The Germany international has been heavily linked with the Bundesliga title holders, as well as Bayern Munich, but Gladbach have confirmed on their official website that the player has decided to join Jurgen Klopp's side on contract until 2017.
"To me it is important to clarify that this is not a decision against Gladbach. I have had a wonderful time here," Reus said. "Borussia have given me the chance to prove myself in the Bundesliga and to develop into the player I am today.
"But I've decided that in the coming season, I'll take the next step and play for a club that contends for the championship and gives me the guarantee to play in the Champions League. This is an opportunity I see in Dortmund."
Reus' future employers were delighted with the signing of the attacker, with Dortmund sporting director Michael Zorc telling the club's official website: "In Marco Reus we sign our absolute preference for an offensive player. We are delighted that Marco has chosen BVB, despite top class competition."
Bayern clarified their interest in Reus earlier this season, but the Bundesliga title holders were able to secure his services for a reported €17.5 million (£14.6m), the value of his buy-out clause.