Rt Revd Brian McGee was consecrated at St Columba's Cathedral in Oban, west Scotland, on Thursday night.
He takes over from Rt Revd Joseph Toal, who served as Bishop of Argyll and the Isles from 2008 until 2014, when he was transferred to become the Bishop of Motherwell.
The new bishop said: "Although it is a challenging vocation, God's grace and the kindness of so many people has greatly encouraged me."
There are more than 10,000 Catholics in the archdiocese of Argyll and the Isles, representing more than one in ten people.
It is there that St Columba, an Irish priest, brought Christianity to Scotland nearly 1500 years ago.
He founded an abbey on the small isle of Iona, which is now a popular Christian pilgrimage site and tourist destination, often referred to as one of the main Scottish symbols of Christianity.
The President of the Bishops' Conference of Scotland, Archbishop Philip Tartaglia, said: "I congratulate Mgr Brian McGee on his nomination and consecration as Bishop of Argyll and the Isles and look forward to welcoming him to the Bishops' Conference.
"When I was Bishop of Paisley, Brian was one of my priests. He was a dedicated pastor and a thoughtful priest.
"I have no doubt that he will make his own distinctive and valuable contribution to the deliberations of our Conference."
