The decision comes as part of a long running legal battle in the case of Coleman v Attridge Law.
Carer and employee Sharon Coleman took her employer,Attridge Law, to court alleging disability discrimination and constructive dismissal, which she believed occurred as a result of her caring responsibilities for her disabled son.
The European Court of Justice decided in July that the EU's anti-discrimination laws, which protect disabled people in the workplace, cover their carers as well. A British employment tribunal had referred the case to the European Court of Justice in 2007.
While public sector workers were able to rely on the Framework Directive immediately to protect their rights, private sector workers could not do so. Instead, they had to rely on the UK 's own domestic discrimination law- the Disability Discrimination Act (DDA), which did not seem to accommodate the ECJ's interpretation of the Framework Directive.
In November 2008, an employment tribunal decided words could be read into the DDA so as to provide the same protection as the Framework Directive, but that decision was not binding on other tribunals.
Attridge Law appealed the decision earlier this year, on the grounds that the tribunal had "distorted and rewritten" the DDA. But today, Mr Justice Underhill, the president of the Employment Appeal Tribunal, dismissed the appeal.
Catherine Casserley, a disability discrimination barristerat law firm Cloisters said: "This finally ends the long running dispute about whether all workers - both in the private sector and the public sector - are protected from direct discrimination or harassment because of an association they may have with a disabled person.
"This decision is binding and will have to be taken into account in future legal cases. Hundreds of thousands of carers amongst others will benefit.
"This decision is also groundbreaking because the judge read into the Disability Discrimination Act whole new subsections in order to provide the necessary protection. As far as I know, it is the first time such a large amount of new text has been added to a domestic statute in order to comply with EC law.
"Private sector employers were warned last November of the need to check their HR policies in the light of this change. If they have not already done so they should consider whether their equal opportunity, anti-harassment, anti-discrimination and absence policies comply with the law in the light of this decision."