On the 28 May 1986, Cardinal Edward Clancy installed Bishop Patrick Murphy as the inaugural Bishop of the newly formed Diocese of Broken Bay. Previously part of the Archdiocese of Sydney, the new Diocese was created as a means of alleviating the difficulties of ministering to a burgeoning Catholic population throughout the Archdiocese.

The name Broken Bay was chosen for its central location in Sydney's northern region, being the mouth of the Hawkesbury River, which divides the north and south of the Diocese.

Beaming across to Broken Bay is the lighthouse situated on the Barrenjoey Peninsula. This lighthouse has become the key symbol in the Diocesan Crest, along with the motto, 'Lumen Christi' - the Light of Christ. Not only does this unify both sections of the Diocese, it is also a striking image of the light of Christ.

Covering an area of 2,763 square kilometres, the 26 parishes, 36 primary schools, 8 secondary schools, 1 K-12, 5 Early Learning Centres, 4 Family Centres and 9 independent Catholic schools that comprise the Diocese of Broken Bay are usually seen as belonging to three separate geographic regions: the Northern Beaches, containing parishes from Avalon to Manly; the North Shore, from Chatswood north to Arcadia and Berowra parishes; and the Central Coast, from Woy Woy to Toukley, Wyong and Warnervale parishes.

All but one Diocesan parishes were established before 1986. In fact the oldest three - Manly (founded 1876), Gosford (1888) and Pymble (1889) - covered most of the present Diocese until 1910.

In 2003 a new parish was formed at Warnervale which incorporates a new K-12 College and extensive facilities for this rapidly expanding area. The Secondary school of St Brigid's, Lake Munmorah, opened in 2014.

With the creation of the Diocese in 1986, came the need to nominate a Cathedral parish where the Bishop would reside as parish priest. Due to its size and centrality, Corpus Christi, St Ives, was established as the liturgical centre, housing the Cathedra (Bishop's Chair), which automatically elevated the beautiful Church to the status of Diocesan Cathedral.

As the needs of a growing Diocese change, so does the way resources are utilised. The Cathedral at St Ives served the Diocese of Broken Bay well for 22 years. Originally a Parish church, the capacity at Corpus Christi for large congregations and liturgies was limited. On 1 February 2008, the Church of Our Lady of the Rosary, Waitara was dedicated as the new Cathedral Centre for the Diocese.

Bishop Murphy retired in 1996, leaving the Diocese well established. His successor was Bishop David Walker, ordained bishop on 3 September 1996.

During his episcopacy, Bishop Walker was committed to promoting a truly Australian spirituality, fostering theological and spiritual education through an experimental understanding of the personal faith journey.

From the beginning Bishop David recognised the way forward for the Church depended on all believers being willing to work together, responding to the opportunities and responsibilities of Christian leadership. He has brought to the Diocese a continued commitment to faith renewal and has invited all to engage in 'grass roots' ownership, fostering greater participation and collaboration in shaping parish and diocesan life.

In May 2011, the Diocese of Broken Bay celebrated its 25th anniversary. In recognition of this milestone, Bishop David Walker, announced that he would be convening a Diocesan Synod in Broken Bay – a time of listening and consultation with the people of the Diocese.

The Synod provided an opportunity to look at what had been achieved as a Diocese over the past 25 years and to provide clear vision and direction for the future.

The motto of the Synod, “Go Make Disciples”, has become a commission, in light of the Synod journey the people of Broken Bay undertook, to continue to build their future - to take up the wisdom, learnings and insights gained, and look toward the future from a personal, parish, agency and Diocesan perspective.
Bishop Walker retired officially on 13 November 2013.On 12 December 2014, Bishop Peter A Comensoli was installed as the third bishop of Broken Bay at Our Lady of the Rosary Cathedral, Hornsby Parish.

Bishop Comensoli had four key focus areas: Youth, Parish Communities, Marriage and Family and Vocations. In his time as Bishop, the Diocese of Broken Bay has started formation for nine seminarians.

After only three and a half years as Bishop of Broken Bay, Pope Francis appointed Bishop Peter A Comensoli as the 9th Archbishop of Melbourne. He was installed as Archbishop of Melbourne on 1 August 2018.
After 15 months of waiting, with Fr David Ranson as Diocesan Administrator, the Diocese welcomed the joyous news that Pope Francis had appointed Most Rev Anthony Randazzo as the fourth bishop of Broken Bay. The announcement was made on 7 October 2019, the occasion being Bishop Anthony’s 53rd birthday.

Broken Bay Diocese is a vibrant community in which participants are challenged and supported to make their faith in Jesus Christ the centre of their lives.