The Spain international made his way to Germany over the summer after being deemed surplus to requirements at Camp Nou.
He had struggled to make his mark in Catalunya, as part of a star-studded squad brimming with attacking talent, but wasted little time finding his feet with Dortmund.
Alcacer has netted nine times in just eight appearances this season, with that return enough to earn him a long-term contract as a €23 million (£20m/$26m) transfer package.
Paco is here for good! ⚽️✍️#Alcacer2023 pic.twitter.com/IiGvei1fYn
— Borussia Dortmund (@BlackYellow) November 23, 2018
“We have informed FC Barcelona today that we will take up option,” Dortmund’s sporting director, Michael Zorc, told the club’s official website.
“Paco is wholeheartedly with us, he has quickly integrated and has become an integral part of our squad.
“He is a striker of high footballing quality and has already decided some important games for us.
“We look forward to many more goals and assists from Paco in the coming years.” added Zorc.
Alcacer spent only two seasons at Camp Nou after joining them in 2016.
He made 50 appearances for the club, but found regular starts hard to come by and managed only 15 goals.
That return could be bettered in just one campaign with Dortmund, with a man who has also caught the eye for his country in recent outings thoroughly enjoying his time at Signal Iduna Park.
“I am very happy in Dortmund, at BVB and in this wonderful team,” Alcacer said after seeing his future resolved.
“Borussia Dortmund was and is exactly the right place for me. I will do everything I can to say thank you for your trust in my performances!”
Paco Alcacer has also been able to earn the trust an loyalty of the Signal Induna faithfuls especially after his winning goal against Bayern Munich.