Rt Rev Sarah Mullally was accompanied at an introduction ceremony on Thursday morning by Most Rev Justin Welby, the Archbishop of Canterbury.
Committing her loyalty to the Queen, she said: "I, Sarah, Bishop of London, do swear by Almighty God that I will be faithful and bear true allegiance to Her Majesty Queen Elizabeth, her heirs and successors according to law, so help me God."
Bishop Sarah became one of the 26 bishops from the Church of England - the state church of England - who serve in the upper house of the Parliament of the United Kingdom.
A former Bishop of Crediton and chief nursing officer, the 56-year-old was installed as the first female Bishop of London during a ceremony held at St Paul's Cathedral in central London earlier this month.
Speaking last December, when her appointment to the role was announced, she said: "I have always had one vocation: to follow Jesus Christ, to know him and to make him known, always seeking to live with compassion in the service of others, whether as a nurse, a priest, or a bishop."
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