The forward has moved to the Foxes for a fee reported to be £25 million, with the 20-year-old signing a five-year deal at the King Power Stadium.
In two full seasons at Man City, Iheanacho played 46 Premier League games and scored 12 goals, but found himself behind Sergio Aguero, Wilfried Bony and Gabriel Jesus in the pecking order.
Iheanacho is eager to get started with Craig Shakespeare's side, and is looking forward to becoming part of the Leicester first team.
“It feels good and I’m happy to be part of this team," Iheanacho told the club's official website.
"I know the ambition of the team and speaking with the manager, he let me know what I need to do – to help the team achieve what they want. I was convinced and I’m happy to be here.
“I was happy speaking with the manager, knowing what the team wants. It gives me more confidence that I will fit in this team and hopefully I’ll achieve a lot.”
Leicester boss Shakespeare is delighted with his new signing, believing that the club have signed one of the best young players in the Premier League.
“It’s a great signing for us," Shakespeare said. "Kelechi is an enormously talented player that has shown a huge amount of promise at every level in which he’s played.
“We’ve tracked his progress for some time, so we know how much quality he’ll bring to the squad. He’s young, he’s hungry, he’s ready for the next stage of his development and I’m delighted that will be with Leicester City.”