Bruce was born in Singapore, the daughter of a self-made Scotsman who worked his way up from post boy to become Managing Director of a division of Unilever. Her mother Rosemary was adopted. She was educated at Gayton Primary School in Heswall, Merseyside, The International School of Milan, and then the sixth form of Haberdashers' Aske's Hatcham College in New Cross, London. It was during this later period that she modelled for the stories in the teenage girls' magazine Jackie.

Bruce studied French and Italian at Hertford College, Oxford, during which period she was a self-confessed punk, and for one week had blue hair.

After leaving university, Bruce joined a management consultant firm for a year, but found the experience depressingly dull:

After this, she worked in an advertising agency for a couple of years, before she met the then editor of Panorama Tim Gardam at a wedding, and pestered him until he gave her a job as a researcher at the BBC on the programme in 1989. After becoming assistant producer on Panorama, she made the change to presenting in 1992 as a reporter for Breakfast News. She then moved to BBC South East, appearing as an occasional presenter and reporter on Newsroom South East. During this time she also appeared on some weekend main BBC News bulletins and reported for Newsnight. From 1994-95 she was a reporter on the BBC2 current affairs programme Public Eye.

In September 1998, she became the presenter for BBC2's The Antiques Show, which was in its fourth series. She presented it for a further two series, showing her interest in presenting Antiques programes nearly a decade before presenting the Antiques Roadshow.

In 1999, as part of a major relaunch of the BBC's news output, Bruce was named secondary presenter of the Six O'Clock News bulletin. She presented the programme as cover for main presenter Huw Edwards as well as regularly on Fridays until a presenter reshuffle in January 2003 to coincide with the retirement of Michael Buerk and the move of Peter Sissons to the BBC News channel. Both Edwards and Bruce moved to presenting the BBC News at Ten and have presented the programme on their respective days since. By becoming presenter, she became the first woman to ever present the bulletin from launch in 2000. More recently, Bruce has once again taken up the role of Friday presenter and main relief presenter on the BBC's Six O'Clock News.

Following the murder of Jill Dando, Bruce took over the position of co-presenter on Crimewatch alongside Nick Ross, until both were replaced by Kirsty Young towards the end of 2007.

On 22 June 2007 it was announced that Bruce was to replace the retiring Michael Aspel as presenter of the Antiques Roadshow in Spring 2008. She appeared in a tongue-in-cheek BBC HD advert in 2008, featuring the show (which is one of the BBC's main programs on its HD service), where she drove a car through a wall, before running towards a falling vase; the car explodes as she jumps to save the vase from crashing.

Bruce also occasionally presents special editions of The Money Programme. In one, she profiled the entrepreneur, Sir Alan Sugar. She said of the experience: "It was a bit like being in front of a hair dryer at very close quarters. He's not backwards in coming forward in his opinions." During the documentary, Bruce - who has always publicly identified herself as a feminist - challenged Sugar's view that women should openly disclose their childcare commitments to a potential employer. Her belief was that if men were not required to declare their ability to meet the demands of their job, it wasn't right that women should do so.

Bruce has often been outspoken regarding her commitment to feminism, expressing concern at a 2006 poll that suggested almost three quarters of women no longer saw feminism as necessary; "The contradictions are still there [in society] which is why I think feminism is still very relevant for me and it's just such a shame that it's become a byword for mustachioed, man-hating women from Lebanon.". Despite her firm views on the subject - including a "disappointment" in women who don't like working with other women - she claims to have softened her more extreme views from her university days, where she once ran a "hilarious" anti-pornography campaign. More recently, she has also contributed to Sky Real Lives' Embarrassing Problems, a show about promoting health and well-being, where she called for women to be as open as possible about reproductive conditions.