Per BBC Radio Oxford, the deal looks close to completion for a very modest fee.
Oxford are only going to pay around £400,000 for the Tunisia international, who will put pen to paper on a long-term deal.
Mizouni is expected to sign for three years, with the 23-year-old coming through the Ipswich academy.
The Paris-born star was on loan at Leyton Orient over the past two seasons, playing 89 games.
"Idris brings a lot of qualities that fit into the profile we were looking for to continue developing the dynamic of our midfield," Oxford head coach Des Buckingham told the club website.
"He has shown over the last few seasons his strong attributes that will allow us to play different ways while being another young player with huge further potential."
Head of recruitment Ed Waldron added: "Idris played against us on two occasions last season and was terrific in both games.
"These games gave us a strong indication of what he could offer, and once matched up with extensive work behind the scenes, we identified Idris as a player who could improve our team.
"We are very pleased with the work we have done in our midfield area and we feel Idris will help develop our on-pitch success, as well as our already existing culture at the club."