Catherine got engaged to Michael Douglas on 31 December 1999 at Aspen, Colorado. The two got married on 18th November 2000 in the Terrace Room of the legendary Plaza Hotel in New York.

Named after her grandmothers: Catherine Fair on her mother's side and Zeta Jones on her fathers. Her character in Traffic (2000) was changed to a pregnant woman, because she was herself pregnant at the time with her son, Dylan. Her wedding ring includes a Celtic motif and was bought in a Welsh town called Aberystwyth.

Catherine was born in Swansea but grew up in the small seaside town of Mumbles in Wales. As a child, she was exposed to a virus that gave her breathing difficulties. This required a tracheotomy surgery, which ultimately left a surgical scar on her neck.