The Foxes achieved great success under Enzo Maresca last season but have been unable to hold on to the Italian manager, who joined Chelsea last week.
Maresca led Leicester to win the English Championship and gain promotion to the Premier League at the first time of asking.
The 44-year-old also helped to elevate Issahaku’s game, having brought him on loan from Sporting Lisbon to the King Power Stadium.
Under Maresca, the 20-year-old enjoyed the most productive campaign in his fledgling career, contributing seven goals and 13 assists in all competitions last season.
This prompted Leicester to trigger the €17 million buy option clause to sign Issahaku permanently from Sporting Lisbon.
However, while the former Steadfast FC winger is set to stay at Leicester, he will be working under Cooper next season.
A statement from the club said Cooper has been appointed on a three-year contract as the Foxes aim to be competitive on their return to the Premier League.
“Steve, 44, has agreed a three-year contract and arrives at King Power Stadium as the Club continues its preparations for our top-flight return, following promotion from the Sky Bet Championship last season,” Leicester announced.
“A manager of Premier League experience following a successful spell with Nottingham Forest, whom he guided to and established in the top flight between 2021 and 2023, Steve has built an excellent reputation in the game for his qualities as a coach and a leader.”
Meanwhile, Issahaku transferred his impressive club form to the Ghana national team, having featured in the Black Stars’ wins over Mali and the Central African Republic (CAR) in the 2026 FIFA World Cup qualifiers in June.
He was named in Otto Addo’s starting line-up against CAR and scored as Ghana recorded a hard-fought 4-3 victory over the Wild Beasts.