Denis Nulty has been ordained bishop of Kildare and Leighlin and said it was a day of celebration.
More than 750 people crowded into the Cathedral of the Assumption in Carlow for the ceremony and others watched on large screens nearby.
Bishop Nulty said: "Today is a celebration of all that is good in a diocese - all that is so enriching in our church; all who gather today represent all that is good about parish and diocesan life."
He said it was a time of transition and profound change in his life.
"The uplifting music, the grace of the liturgy, the decoration of the Cathedral continue a proud Kildare and Leighlin tradition, which speaks volumes to native and visitor alike this day. To everyone I simply say thanks," he said.
He had been a parish priest in St Mary's in Drogheda in Co Meath before his appointment as bishop earlier this year.