Rowett, who was sacked as Oxford boss two months ago, has signed with the Foxes to the end of the season. He took training for the first time on Wednesday morning.
"I'm really proud to be the new Leicester City manager and to have the opportunity to work with and lead a really talented group over the coming months," Rowett told Leicester's website.
"It's very clear to us all what needs to be achieved between now and the end of the season and the work begins immediately.
"I'm looking forward to building connections with the players, with the staff at the club and with the fans - all of which will be vital to helping us secure the results we need."
Rowett had two years as a Leicester player after joining from Birmingham City in 2000.
Leicester are third from bottom in the Championship, two points adrift of the safety line with 14 games left.