The collegiate parish church of St Saviour was designated as a cathedral in 1905 when the Church of England Diocese of Southwark was created.
The nearby early-18th-century church of St Thomas became the new cathedral's chapter-house.

The cathedral stands in an area heavily damaged by German bombing during the Second World War.
 The total number of bombs dropped on Southwark between 7 October 1940 to 6 June 1941 alone was 1,651 High Explosive Bombs and 20 Parachute Mines.
On 20 February 1941 it was reported (after being unrestricted by the ministry of information) the cathedral had been damaged by a bomb.
Shrapnel damage is still visible on the outside of the building to this day.

There are memorials to Isabella Gilmore and the victims of the Marchioness disaster and monuments to Nelson Mandela and Desmond Tutu.
 In 2001 Mandela opened a new northern "cloister" on the site of the old monastic one, with a refectory, shop, conference centre, education centre and museum.
In 2002, these Millennium buildings received an award for being one of the best new buildings of the year.

On 16 November 1996 the cathedral became a focus of controversy when it hosted a twentieth-anniversary service for the Lesbian and Gay Christian Movement.
Jeffrey John, the openly gay Dean of St Albans and former bishop-elect of Reading, was Canon Theologian of Southwark.

After the introduction of civil partnerships and, later, of civil marriage for same-sex couples in England, the Cathedral announced that "same sex couples are welcome to approach the clergy with regard to preparation and prayers when entering a Civil Partnership and for continuing support and counsel within their relationship ... couples approaching the clergy should expect a warm welcome and affirmation".
The Cathedral now says, "Southwark Cathedral is an inclusive community where LGBTi+ people are welcomed and affirmed.
The clergy would be delighted to help you to prepare prayerfully for your Civil Partnership."

On 18 July 2017 the conservative organisation Anglican Mainstream announced that Southwark Cathedral had held what it described as a 'wedding-style reception' following the civil partnership ceremony of the Revd Dr Helen Orchard, team vicar of St Matthew's, Wimbledon, and the Revd Canon Leanne Roberts, canon treasurer of the cathedral and director of vocations and diocesan director of ordinands for the diocese.
The event, which included a celebration of the Eucharist, was attended by the Very Revd Professor Martyn Percy, Dean of Christ Church, Oxford and his wife the Revd Canon Dr Emma Percy, chaplain of Trinity College, Oxford.
The collegiate parish church of St Saviour was designated as a cathedral in 1905 when the Church of England Diocese of Southwark was created. The nearby early-18th-century church of St Thomas became the new cathedral's chapter-house.
The cathedral stands in an area heavily damaged by German bombing during the Second World War.  The total number of bombs dropped on Southwark between 7 October 1940 to 6 June 1941 alone was 1,651 High Explosive Bombs and 20 Parachute Mines. On 20 February 1941 it was reported (after being unrestricted by the ministry of information) the cathedral had been damaged by a bomb. Shrapnel damage is still visible on the outside of the building to this day.
There are memorials to Isabella Gilmore and the victims of the Marchioness disaster and monuments to Nelson Mandela and Desmond Tutu.  In 2001 Mandela opened a new northern "cloister" on the site of the old monastic one, with a refectory, shop, conference centre, education centre and museum. In 2002, these Millennium buildings received an award for being one of the best new buildings of the year.
On 16 November 1996 the cathedral became a focus of controversy when it hosted a twentieth-anniversary service for the Lesbian and Gay Christian Movement. Jeffrey John, the openly gay Dean of St Albans and former bishop-elect of Reading, was Canon Theologian of Southwark.
After the introduction of civil partnerships and, later, of civil marriage for same-sex couples in England, the Cathedral announced that "same sex couples are welcome to approach the clergy with regard to preparation and prayers when entering a Civil Partnership and for continuing support and counsel within their relationship ... couples approaching the clergy should expect a warm welcome and affirmation". The Cathedral now says, "Southwark Cathedral is an inclusive community where LGBTi+ people are welcomed and affirmed. The clergy would be delighted to help you to prepare prayerfully for your Civil Partnership."
On 18 July 2017 the conservative organisation Anglican Mainstream announced that Southwark Cathedral had held what it described as a 'wedding-style reception' following the civil partnership ceremony of the Revd Dr Helen Orchard, team vicar of St Matthew's, Wimbledon, and the Revd Canon Leanne Roberts, canon treasurer of the cathedral and director of vocations and diocesan director of ordinands for the diocese. The event, which included a celebration of the Eucharist, was attended by the Very Revd Professor Martyn Percy, Dean of Christ Church, Oxford and his wife the Revd Canon Dr Emma Percy, chaplain of Trinity College, Oxford.
Southwark Cathedral