[3] She studied at the University of Reading, graduating in 1984 with a Bachelor of Arts (BA) degree in linguistics and language pathology.

After six years as a paediatric speech therapist in the National Health Service, she left her job to train for ordination in the Church of England.

[12] In September 2013, Treweek was elected as one of eight "participant observers" of the House of Bishops representing the South East of England.

[27] Then, on 26 October 2015, she was introduced to the House by Justin Welby, Archbishop of Canterbury, and Richard Chartres, Bishop of London.

[33] In November 2023, she was one of 44 Church of England bishops who signed an open letter supporting the use of the Prayers of Love and Faith (i.e. blessings for same-sex couples) and called for "Guidance being issued without delay that includes the removal of all restrictions on clergy entering same-sex civil marriages, and on bishops ordaining and licensing such clergy".

[34] Following Justin Welby's decision in November 2024 to stand down as Archbishop of Canterbury due to his failing to act after becoming aware of child abuse by John Smyth, who was associated with the Church of England, Treweek said that resignation was the right thing to do, commented that the position was "very, very difficult ... stepping into the structures that do need to change", and said that the affair had shown the "very clunky governance we have within the Church of England ... We do not have quick decision making, there are too many different levels, groups, involved.

[35] In 2006, she married Guy Treweek; he is a Church of England priest and was priest-in-charge of two ancient City of London parishes at the time of her appointment to the episcopate.

On 8 July 2016, Treweek received an honorary doctorate (Hon DLitt) from her alma mater, the University of Reading.