The striker has signed for an undisclosed fee with both clubs agreeing to silence, while Boyd himself has penned a deal through to June 2018.
Another reinforcement for the battle to beat the drop
The 25-year-old forward looks to be finally over his knee injury woes that have limited him to just a handful of appearances since joining Leipzig.
He featured just 17 times across two-and-a-half seasons for the Red Bull Arena outfit, following his move to the then 2. Bundesliga side from Rapid Wien.
Having previously played for Borussia Dortmund and Hertha BSC, Darmstadt is now the fourth German club he has turned out for.
Now with fitness concerns behind him and the chance to kick on and show the form that earned him a return to his country of birth.
Darmstadt have been busy in the January window and despite the early end to Laszlo Kleinheisler's loan, the Lilies have brought in two other new faces.
Markus Steinhöfer arrived on a free last week, with Sidney Sam being acquired on a loan deal until the end of the 2016-17 season.
Frings and Boyd have their say
Speaking to the Darmstadt club website after the deal was made official, head coach, Torsten Frings and Boyd himself gave their thoughts on the move.
Frings said, "We are very pleased that Terrence Boyd has decided to come to us and would like to continue his journey with us."
Boyd explained, "I'm excited that the transfer to Darmstadt 98 has worked out and will immediately take action in order to make the impossible, possible."
The American international will be raring to go on Saturday, as they welcome 1. FC Köln to the Jonathan-Heimes-Stadion-am-Böllenfalltor.
Quotes via SV Darmstadt 98.