Tanith was born in London and was educated at Lady Eleanor Holles School, Surrey before moving to New York City in her early teens.
She attended high school there before returning to study English and French at Durham University, and later Periodical Journalism at City University.
Tanith started her career as a news reporter, becoming a crime correspondent on the Brighton Evening Argus before joining the Daily Mirror.
After several years as a feature writer undertaking investigations, celebrity interviews and backgrounders, she joined the Features Desk, first as Woman's Editor, and then Features Editor.
Soon after the birth of her first child, Tanith was awarded Consumer Journalist of the Year – and later that year moved to New York as the Mirror's US Editor, a position she held jointly with her husband Anthony Harwood.
While in New York, she joined American Media as an Executive Editor, helping to re-launch the company's biggest magazine title.
On her return to the UK in 2005, Tanith wrote her first book, the biography of Russell Brand. It was followed by A Mother's Love, a prose collection on motherhood and How to Be an Amazing Mum – When You Just Don't Have the Time. Her latest book is Where Has My Little Girl Gone?
She has also been nominated as National Newspaper Health Writer of the Year as well as the UK Press Gazette Scoop of the Year for her investigative journalism.
Tanith lives in North London and now combines writing books with journalism.