She was born (as Laura Ruth Sadler) in Ascot, Berkshire, and took up television acting as a young girl. She was spotted as a future talent at the age of 6 by Dustin Hoffman, who had seen her in a play. After the play had finished Dustin went backstage to meet the then child actress. Before joining the cast of Holby City, her best-known role had been as the character Judi Jeffreys in the children's television series Grange Hill from 1997 to 1999. In a tragic irony, her Grange Hill character was killed after slipping and falling out of a burning building, paralelling her real life death 4 years later.

In 1996 she starred in the feature film Intimate Relations alongside Julie Walters, where she played a Lolita-like girl with a crush on her mother's adulterous lover.

She joined the cast of Holby City, a spin-off series from the long-running BBC medical drama series Casualty, in the show's third series.

In the early hours of June 15, 2003, she fell 40 feet (12 metres) from the rear window of a block of flats in Holland Park, an area of west London, apparently having previously taken alcohol and cocaine. The building was the home of her boyfriend, fellow Holby City actor George Calil. She suffered severe head injuries, and never regained consciousness. She died at Charing Cross Hospital on June 19, after a decision by her family the previous day to have her life support system turned off.

Her boyfriend Calil, aged 30, who played her character's drug-dealing boyfriend Sean Hunt in Holby City, was arrested for questioning, before being released on bail. On June 26 police announced that the death was being treated as accidental and no further action would be taken.

Laura Sadler continued to feature in pre-recorded episodes of Holby City after her death. Laura's mother took part in writing her daughter's character Sandy out of Holby City, in which she won the lottery and subsequently emigrated.