A group of art and history experts who worked at the National Gallery have won a bid to be given workers' rights.
The 27 educators, who call themselves the NG27, gave talks, lectures and workshops at the central London museum until October 2017.
They said they were not given any paid holiday, sick pay, pension or maternity pay despite paying taxes through the payroll.
The National Gallery had claimed the educators were all freelancers.
After an employment tribunal in central London, Judge A M Snelson ruled on Thursday it was "unsustainable" for the gallery to describe the workers as self-employed.
The NG27 also made claims of unfair dismissal, but these were dismissed by the judge.
The case is thought to be the first in the public sector to address concerns about workers' rights after a flurry of cases against companies in the "gig economy" such as Uber.
One of the claimants, Karly Allen, worked as an educator at the in Trafalgar Square gallery for 18 years.
Ms Allen, 44, who lives in Brixton, south London, said: "This judgement cannot take away the fact that we have lost our jobs and the close relationship with the gallery which we loved.
"It does go some way to acknowledging the losses we have suffered and our contribution to the life of the gallery."
Ms Allen thanked supporters for the £77,000 pledged on a crowd-funding page to cover the legal costs of the case.
Marie van der Zyl, a member of the claimants' legal team, said: "The world of work is changing and there will be many individuals who are unsure of their status and rights.
"This case gives those individuals hope."
She said the group would work out whether any backdated holiday pay was owed and "actively consider" whether to appeal against the ruling that the claimants should be classed as workers, but not employees.
What's the difference between employees and workers?
Employees have more employment rights than workers, according to the Advisory, Conciliation and Arbitration Service.
These include protection against unfair dismissal, redundancy pay and parental leave.
Both, workers and employees are entitled to holiday and sick pay, minimum wage and protection against discrimination.
A spokesman for the National Gallery said it "welcomed" the clarification.
"It is important to state that this case should not be likened to the 'gig economy' debate that has been in the news recently," he said.
"We have taken a deliberate choice to move towards a model that offers people secure employment, with additional pension and worker benefits."