Moussa was headed towards Najaf on Saturday to meet Grand Ayat Allah Ali al-Sistani in a quest to foster national dialogue and ease sectarian tension.
Moussa had led a large delegation to Najaf early on Saturday to meet al-Sistani.
"During [the meeting], I got [al-Sistani's] support, which made me glad," Moussa said.
The Arab League chief had already held discussions with the influential Sunni Association of Muslim Scholars and several members of the Iraqi government when he arrived in the capital Baghdad on Thursday as part of an Arab League effort to ease sectarian tensions in the country.
It was his first visit to the country since the March 2003 US invasion and unseating of Saddam Hussein.
Moussa has strongly condemned violence in Iraq in a bid to overcome Shia and Kurdish suspicions that the Arab League supported Saddam's government prior to the invasion and was now tilting in favour of Sunni Arabs.
Nevertheless, Iraqi leaders did not commit to a reconciliation conference that Moussa is trying to organise, the first major intervention by the Arab League.
But Prime Minister Ibrahim al-Jaafari said on Thursday that he had no objection to the league's proposed national dialogue as long as it did not include "terrorists who have shed blood and high-ranking Baathists" from Saddam's ousted government.
Awaiting poll outcome
Meanwhile, Iraqis are still waiting to know the outcome of the country's 15 October constitutional referendum.
Amr Moussa also met the
Association of Muslim Scholars
They probably will not learn the final results until next week.
Initial returns indicated that the charter passed, with Sunni Arabs opposing it and levelling accusations of fraud.
Electoral officials are auditing unusually high yes votes in some areas to ensure there were no irregularities.
The election commission announced turnout figures on Friday, saying 9,775,000 Iraqis cast ballots - or 63% of registered voters. That was higher than January's parliament elections, in which 60% of Iraqis participated, including fewer Sunni Arabs.