Gladbach will pay a base fee of €3.5 million with add-ons that can take the total package to €4 million, according to Sky Germany. Darmstadt have also secured a sell-on clause. Lidberg has signed a four-year contract running until June 2030.
The 27-year-old scored 17 goals and contributed three assists in 30 second-division appearances last season, starting every match. It was the latest instalment in a sustained run of productivity in German football — across 58 appearances for Darmstadt in all competitions, Lidberg contributed 31 goals and nine assists.
Gladbach sporting director Rouven Schröder was direct in his assessment of what the club are acquiring.
"Isac is a goal threat, physically strong and knows how to hold his own in challenges. Combined with his dynamism and mentality, he represents the picture of an aggressive centre-forward," Schröder said.
"During our discussions we realised how much enthusiasm and ambition he has for the challenges at Borussia, and we are pleased to have filled another important squad position with a high-quality player early in the window."
Lidberg himself spoke of a childhood connection to the Bundesliga.
"When I found out about Borussia's interest, I was immediately enthusiastic," he said. "Borussia is a big club with an impressive history. As a child I followed the Bundesliga and always watched Borussia matches. That's why I didn't need much convincing."
Lidberg joined Darmstadt from FC Utrecht in the summer of 2024 for €1 million. The club now recoup up to four times that outlay despite a season that ended without promotion for the Darmstadt side, who narrowly missed out on returning to the top flight.
Borussia Monchengladbach finished twelfth in the Bundesliga last season and will hope Lidberg's goal record translates upwards.