After signing centre-back Kostas Manolas earlier in the week, Roma confirmed the capture of Greece international team-mate Holebas - capped 26 times at international level - for a €1million fee following Saturday's opening Serie A win over Fiorentina.
Holebas has penned a three-year deal with last season's Serie A runners-up after playing an integral role in Greece's run to the last-16 at the World Cup in Brazil.
The 30-year-old's move to Roma ends his trophy-laden four-year spell with the Greek giants, having arrived from German outfit 1860 Munich in 2010.
He won the Greek Superleague title in all four seasons at the Karaiskakis Stadium, while he also lifted back-to-back Greek Cup trophies.
Holebas is expected to be the final piece of business from coach Rudi Garcia in the transfer market following the arrivals of Juan Iturbe, Ashley Cole, Urby Emanuelson, Salih Ucan, Leandro Paredes, Alan Arario, Seydou Keita, Davide Astori and Manolas.