Moroccan defender Benatia, who has been with the Roma squad for several days and been a Giallorossi player in all but name, joins from Udinese for €13.5m and has signed a five-year contract that will tie him to the club until 2018.
As part of the deal, Udinese have taken Valerio Verre and Nico Lopez on co-ownership deals. The negotiations of the co-ownerships are believed to have been the factor that held up the deal, but Roma have ensured that they at least retain stakes in the highly rated pair.
Roma have also completed a move for young Polish keeper Lukasz Skorupski from Gornik Zabrze, for whom Skorupski has played 56 times in the last two seasons.
The 22-year-old was signed for €890,000, and has put pen to paper on a four-year deal with an option for the club to extend it a further year to 2018.