Sadiq had been awaiting work permit clearance before he was able to complete a switch that Steven Gerrard believes will add power to the Ibrox attack.
Umar Sadiq has signed a season-long loan deal with Rangers.
"At 21-years-old Umar has already impressed with Roma and on loan, most notably during a spell at NAC Breda last season".
The 22-year-old midfielder is the eighth signing of the summer window for new manager Steven Gerrard, subject to global clearance. Coulibaly told Rangers TV.More news: Perisic hails 'dream' goal as Croatia reach final
"I sat the young lads down on day one and told them they would come over to Spain and it was down to them to mix it with the senior players and let them know you're here to challenge them", he said.
"At the moment he is still a Roma player but it has been well documented that I am a fan, but it's just a case of watch this space", he said. "I know the team are in the Europa League and I know there is a big rivalry with Celtic".
Gerrard remains in the market for further reinforcements this summer and a move for Mali worldwide midfielder Lassana Coulibaly is still ongoing at present.
"He asked me if I wanted to join his team, and I said yes, although I was anxious it wasn't actually Gerrard (on the phone)!" the Malian said.More news: Los Angeles woman arrested for beating Mexican man with a brick
Speaking exclusively to RangersTV Sadiq said: "It is very good to be here, it has been good so far and I can't wait to start".
"He can help me to develop".
Allan McGregor, Jon Flanagan, Scott Arfield, Jamie Murphy, Connor Goldson, Nikola Katic and Ovie Ejaria all joined earlier in the window.More news: Stormy Daniels arrested at Ohio strip club, says her lawyer Avenatti