Katharine McGregor was born in Brisbane in 1903. She attended Brisbane Girls' Grammar School and won an Open Scholarship to study at Queensland University. In 1920, she was one of three students to commence her studies in Classics, which she completed three years later with first class honours.

After graduating from university, Katharine worked as a solicitor with her father, J.G "Jock" McGregor, at his practice McGregor McGregor & Atthow. Katharine was admitted as a barrister on 5 October 1926 and was the first woman to be admitted to the Queensland Bar. She continued to work as a solicitor and after the death of her father, Katharine set up her own practice in Queen Street.

Katharine eventually left the law to become a private teacher in Classics-Greek and Latin. She also wrote and marked Classics papers for high school and university students.

Katharine never married and she led a very quiet life until her death on 25 June 1979, at the age of 76.