Archbishop Louis Sako was enthroned on Wednesday as the new patriarch of the Iraq-based Chaldean Church during a mass in Baghdad broadcast on national television.
He replaces Emmanuel III Delly, who retired in December after reaching the mandatory retirement age of 85 in the church, which is the largest Christian community in Iraq and recognises the authority of the pope.
The ceremony was held in the Mar Yusuf cathedral in the Karrada area of central Baghdad, with main roads blocked off by security forces.
"I will work with Muslims and Sabeans (a small minority community) to achieve... justice, freedom, equality and commitment to dialogue" with Sunni and Shiite Muslim clerics, Sako later told AFP in a telephone interview.
Sako, who was archbishop of Kirkuk, takes the title of Patriarch of Babylon of the Chaldeans. He is seen as pro-Kurdish and has favoured co-operation with Muslim leaders.
The Chaldean church, which has 700,000 followers worldwide and uses Aramaic -- the language that Jesus Christ spoke -- is one of the oldest Christian communities in the world.
But along with other Iraqi Christians, it suffered persecution, forced flight and killings in the aftermath of the 2003 US-led invasion.
Before 2003 more than a million Christians lived in Iraq. Now they number around 450,000.
According to the UN High Commissioner for Refugees, many thousands fled after 44 worshippers and two priests were killed in an attack on a Syriac Catholic church in Baghdad on October 31, 2010, an atrocity claimed by Al-Qaeda.
Between 2003 and May 2012, some 900 Christians were killed, while 200 were kidnapped, tortured and ultimately released for exorbitant ransoms, according to the Hammurabi Human Rights Organisation in Iraq.
Sako was elected on February 1 by bishops from Iraq and other parts of the Middle East, as well as areas of North America and Europe with large Iraqi diasporas, at a synod held in Rome for security reasons.