Sally Brown, a housing association worker, successfully sued the Department of Social Security for sick pay after she was forced to leave work for six months with an injured neck.
'I am pleased it is all over and that I have been able to set a precedent for other people in my position,' said Mrs Brown.
Mrs Brown worked for Granta Housing Association for nine months before she fell ill in 1992, but was refused sick pay on the basis that her contract expired at the end of every day.
The ruling could affect tens of thousands of casual workers, said David Thomas, legal officer at the Child Poverty Action Group, which along with Unison supported Mrs Brown in her claim.
To qualify for statutory sick pay a person now has to have worked for at least part of each week over a three-month period, and earned an average of more than £61 a week, according to Mr Thomas.
Casual workers of more than three months' standing are now entitled to a minimum of one week's notice. Ms Brown has yet to settle her claim for £1,200, and her case has been referred back to the Social Security Appeals Tribunal.