The 29-year-old defender joins the capital club from Dutch side PSV for a reported €5 million and has signed a four-year contract through 2021.
“I am very happy to sign for Roma,” Moreno told Roma’s official website. “This represents an important step up in my career.
"I hope I can show my individual qualities and contribute to the overall success of the team.”
Moreno had spent the last two seasons with PSV alongside Mexico team-mate Andres Guardado and helped the side win the 2015-16 Eredivisie title, having previously won it in 2010 with Louis van Gaal's AZ.
“Moreno has been a target of mine for a long time, and fortunately now the circumstances are right for him to join us at Roma,” Roma’s sporting director Monchi said.
“This is a central defender with a lot of international experience, and he perfectly fit the profile we were looking for.”
Internationally, Moreno has been capped 79 times for Mexico, scoring two goals. He was part of his country’s 2011 Gold Cup winning side and appeared in the 2014 World Cup for El Tri. Moreno is part of Mexico’s roster for the upcoming Confederations Cup in Russia.