Heather Renwick Brown was born in 1929, the daughter of a teacher and a Scottish coalminer.
Winning a scholarship to read classics at Girton college, Cambridge, she developed her acting skills through student drama. After a spell at Selfridges as a management trainee, she married the diplomat, Geoffrey Brigstocke and took a part-time post as classics teacher at Godolphin and Latymer school while raising her family.
When her husband was posted to Washington in 1961, she taught Latin at the National Cathedral School for Girls while performing the duties of a diplomat's wife.
Back in England in 1964, she became head of Francis Holland school, central London, and nine years later she was appointed high mistress of St Paul's.
Her husband was killed the same year in an aircraft accident over Paris.
A fierce advocate for the special opportunities offered by girls' schools, she taught her charges that everything was possible for them. While still high mistress she served as a non-executive director of London Weekend Television and sat on the committee of the Automobile Association. After retiring from St Paul's, she was awarded with a peerage.
There followed non-executive directorships on the board of Times Newspapers, Burberry's, Great Universal Stores and a role as a member of the Health Authority. She was chairman of the English-Speaking Union for six years.
Baroness Brigstocke was killed last Friday in a road accident in Greece while raising funds for Home-Start International, a charity that works to support children in danger of being taken into care.
She is survived by her husband Lord Griffiths, whom she married in 2000, and by her daughter and three sons.
The writer is president of the Girls' Schools' Association