The drivers claimed that the private hire firm acted unlawfully by denying them sick pay, a guaranteed minimum wage, holiday pay and breaks.
The London Central Employment Tribunal ruled in their favour, a decision which could affect thousands of other people who work for companies with similar business models.
Nigel Mackay, who represented the drivers, described the ruling as “a groundbreaking decision”.
Uber said it would appeal the judgement.
The tribunal centred on whether drivers with Uber are employees.
Uber insists its 40,000 drivers are “partners” and self-employed, meaning they are not entitled to holiday pay and other benefits.
But drivers argue they are actual employees of the organisation, rather than independent operators running their own businesses.
Mr Mackay claimed Uber drivers work very long hours “just to earn enough to cover their basic living costs”.
He said: “(The ruling) will impact not just on the thousands of Uber drivers working in this country, but on all workers in the so-called gig economy whose employers wrongly classify them as self-employed and deny them the rights to which they are entitled.”
The “gig economy”, in which self-employed workers take on temporary positions, has boomed in the UK.
According to official figures, the number of people registered as self-employed rose to 4.8 million in August this year – accounting for 15% of the UK population.
Uber has two million users in London who make around one million trips a week.
The GMB’s legal director Maria Ludkin labelled the gig economy “old-fashioned exploitation under newfangled jargon”.
She said: “Uber drivers and thousands of others caught in the bogus self-employment trap will now enjoy the same rights as employees. This outcome will be good for passengers too.
“Properly rewarded drivers are the same side of the coin as drivers who are properly licensed and driving well maintained and insured vehicles.”
On the ruling, Uber’s UK general manager Jo Bertram said: “The overwhelming majority of drivers who use the Uber app want to keep the freedom and flexibility of being able to drive when and where they want.
“While the decision of this preliminary hearing only affects two people we will be appealing it.”
Uber has been accused of violating employment rights in other countries.
In April, drivers in California and Massachusetts filed a lawsuit against the company claiming they had been wrongly classified as independent contractors.
Before the case went to trial the firm offered to pay $100m (£82.1m) to the drivers to settle the lawsuit, but a court ruled the sum was “not fair, adequate or reasonable”.