And Ranieri will now be hoping Ndidi, 20, ends his search for N'Golo Kante's successor.
Kante has been sorely missed by the Premier League champions since leaving for Chelsea last summer but Ndidi, who joins from Belgium side Genk subject to a work permit, could fill his shoes.
Claudio Ranieri spent £68million bolstering his title-winning squad and has wasted no time in opening the chequebook again once this transfer window opened.
Defensive midfielder Ndidi has been capped five times so no complications are expected and a deal should be wrapped up later this week.
Ndidi, 20, has agreed a five-and-a-half year deal after passing his medical. He had been on the radar of a number of clubs but Leicester have moved first.
Signed by Genk during former manager Alex McLeish's time in charge, he has burst onto the scene this season.
He helped Genk secure their place in the Europa League knockout stages and is rewarded with a move to the King Power Stadium.
In the group stages of the tournament, Ndidi made more tackles and interceptions than any other player.
Ndidi joins his international team‑mate Ahmed Musa at Leicester and both will be available during the Africa Cup of Nations because Nigeria failed to qualify.