Kristin's father was a Royal Navy pilot, but he was killed in a flying accident when she was a small child. Her mother re-married, but Kristin's new step-father soon died in the same way, and the children (Kristin is the eldest of five) were brought up by their mother in Dorset, in the west of England.
Kristin went to the Central School of Speech and Drama, in London, for a year, but it didn't work out. She began to train to be a school-teacher, but a visit to Paris led to a job there, and she soon got into the École Nationale des Arts et Technique de Théâtre, again training to be an actor. At the beginning of her career, she worked more in French than in English-language productions.
Kristin is married to Dr François Oliviennes
. They have three children, Hannah, Joseph and George, and live in France. One of Kristin's sisters, Serena Scott Thomas
, is also an actress.