Holman started her acting career in the 1988 television film The Rainbow based on the novel by D.H. Lawrence, directed by Stuart Burge.

In 1991, she played Iris Bentley, sister to Derek Bentley, played by Christopher Eccleston, in the film Let Him Have It, and in 1992, she voiced Juliet in the Shakespeare: The Animated Tales adaptation of Romeo and Juliet.

She played Harper in the Royal National Theatre's production of Tony Kushner's Angels in America in November 1993. In 1995, Holman was cast as Dr Laura Hobson in the crime drama series Inspector Morse, where she continued to play that part until 2000 when the series ended.

Holman was nominated for a 1997 Laurence Olivier Theatre Award for Best Actress in a Supporting Role in 1996 for her performance in Who's Afraid of Virginia Woolf?. She appeared in two episodes of Midsomer murders as two different characters. The episodes are entitled Country Matters (2002) and Ring Out Your Dead (2005).

Holman was married to Director Howard Davies. They married in April 2005 in Stratton, Cornwall and were together until his death in October 2016. She has stepchildren and stepgrandchildren from her husband's previous marriage. She supports ending violence against girls, contributing to Plan UK, part of the world's biggest campaign for girls' rights. Holman remains good friends with Kevin Whately and Laurence Fox.

In 2006, Holman reprised her role of Dr. Hobson in the series Lewis, which series ended in 2015. She appeared in all 42 episodes.

Holman teaches drama at the Guildhall School of Music and Drama and has directed six episodes of Doctors in 2010 and two episodes of Holby City in 2012.

In October 2013 she played the role of Liz in the Tricycle Theatre production of the Moira Buffini play Handbagged, and in 2015, Holman appeared in the film Suite Francaise. From April to May 2015, she appeared as Myra Bolton in Doris Lessing's play, Each His Own Wilderness, at the Orange Tree Theatre in Richmond, London.