The 2400 female claimants now stand to gain tens of thousands of pounds each in back-dated pay.
Lawyers, campaigners and the trade union Unison said South Lanarkshire's efforts to bring women and men together under a single status pay system has been effectively ruled as not fit for purpose.
The Employment Tribunal has said the local authority has not complied fully with subsequent advances in equality law.
It was the first council in Scotland to introduce a single-status agreement for both sexes. Now the tribunal has ruled its Job Evaluation Scheme does not comply with the provisions of the Equal Pay Act 1970.
Individual claimants can now compare pay with colleagues employed in work of equal value and the council must now explain all pay differences on an individual basis.
One solicitor involved with the claims said some workers could start to receive cash by the end of this year, with some women with 12-year claims seeing a disparity with male colleagues of £5000 a year.
However, Carol Fox, director of Fox Cross Solicitors, which is representing the claimants, said the process could drag on further if South Lanarkshire appeals.
Successful claims could see the council face a financial black hole running into millions of pounds, at a time of unprecedented cuts to the public purse.
Glasgow City Council, whose claims ran into to tens of millions of pounds, was forced to use up much of its reserves and embark on major savings programmes to pay for the claims.
Ms Fox said: "I'm absolutely delighted for all the claimants who have waited more than six years for this result. They have worked hard as cleaners, catering assistants and carers and have watched in dismay as all other councils reached settlements. South Lanarkshire Council ploughed on defending the indefensible at taxpayers' expense.
"Our 2400 clients hope there will now be a full inquiry regarding the actions and decisions of councillors and trade union officials in South Lanarkshire over the past decade."
Mike Kirby, Unison's Scottish secretary, said: "It is clear from the tribunal ruling the council has some work to do if it is to deliver equality in a transparent manner."
A South Lanarkshire Council spokesman said: "This is a complex judgment reflecting the fact two-and-a-half years' worth of evidence was heard in this case. We will be taking time to analyse the content before considering our next course of action. Crucially, the tribunal did not find our job evaluation scheme to be sex discriminatory."