The wing-back played 13 times on loan for Bolton in the 2020/21 campaign but was recalled by his parent club Luton Town in the winter window.
He since had loan spells with Northampton Town and MK Dons in League One before signing a permanent deal with Paul Warne’s Rotherham United last summer.
Kioso struggled with injuries last season and ended up playing just 13 times for the Millers, falling out of favour with Warne’s successor, Matt Taylor.
He still has two years left on his contract with Rotherham but has dropped back into League One with Peterborough in the hope of securing more game time.
Posh were beaten play-off semi-finalists last season and transfer listed several of their more experienced players in pursuit of a young, more energetic squad this time around.
“I feel this is the right club for me,” Kioso said. “I know a few of the lads already, in fact I was speaking with Kabongo Tshimanga yesterday and he was saying what a good club it is and I can’t wait to get started. I like to defend, but also in my position, you need to be able to do the attacking side of the game too and I really enjoy that aspect too.
“I wanted to get the deal done before the season starts, I have been involved for Rotherham so fitness wise I am fine, I can settle quickly and I am looking forward to it.”