The 24 year old joined in June 2022, and made 25 appearances for the Millers, spending the first half of last season on loan at Peterborough, with 25 outings and one goal.
Kioso didn't want to rejoin the Millers from the Posh and Peterborough were hoping to secure his services but the defender has opted to stay in the Champrionship.
“The reason I wanted to sign is because it’s a club that knows what direction they want to go in. I want to be part of that as the club have full belief and I do too. I want to help the team get stronger. There is a great team here and I need to show the boys why I deserve to be here.” he told Luton Today.