The Frenchman heads to Anfield on a six-year contract after Liverpool stepped up their pursuit of another forward for Arne Slot's squad.
The Reds will reportedly pay Frankfurt a guaranteed £69 million fee up front, plus £10 million in performance-related add-ons.
Ekitike prompted Premier League interest after recording 22 goals and 12 assists across all competitions last term, while being named in the Bundesliga Team of the Season.
Newcastle were one of the sides keen on the 23-year-old and saw a £70 million offer turned down by Frankfurt before backing away from a deal.
Liverpool had considered a move for Newcastle star Alexander Isak and communicated their willingness to pay £120 million for the Sweden international.
However, they were told he would not be for sale and set their sights on Ekitke instead, wrapping up for the club's pre-season tour of Hong Kong and Japan.
Ekitike joined Frankfurt on an initial loan from Paris Saint-Germain in February 2024, before the move was made permanent two months later.
Internationally, he has not yet been capped at senior level for France, but has played five times for the Under-21 side.
Ekitike joins a refreshed Liverpool squad preparing to defend their Premier League crown.
Florian Wirtz, Jeremie Frimpong and Milos Kerkez have already been recruited, while goalkeeper Giorgi Mamardashvili joined after an agreement last summer.