Songs of praise are set to echo out a little wider this morning, as Auckland's Holy Trinity Cathedral celebrates its official completion.

The Bishop Selwyn Chapel, which adjoins the large cathedral, will be opened today - marking the church's final building project since the first stone was laid in the 1950s.

Dean of Holy Trinity Cathedral, the Very Reverend Jo Kelly-Moore said Auckland leaders and city councillors will join the congregation this morning to celebrate and dedicate the chapel as a sacred place.

"Cathedrals are long journeys in their construction and the foundation stone of our cathedral was laid in 1957, so 59 years later a full stop is put and it's a great day of celebration."

She said a prayer of blessing will be said by Bishop Ross Bay to dedicate the chapel as a sacred space, and there will also be the official opening.

Ms Kelly-Moore said there are many in the regular congregation who've been there for all phases of its building, so it's a special day.

The chapel has entirely glass walls, and a gilded ceiling.