"For such a relationship to exist, the courts have determined that there must be, at a minimum, an obligation for an employee to perform work when it is demanded by the employer."
Ms Parker said as a result of her investigation "the Fair Work Ombudsman will not take compliance action in relation to this matter".
Uber - which considers drivers to be independent contractors - welcomed the decision and said "being your own boss" was the main reason people drove for the company in the first place.
"They choose if, when and where they drive," an Uber spokeswoman told AAP in a statement.
"More than 90 per cent of driver-partners in Australia tell us flexibility is the key attraction to using the Uber app."
But the Ride Share Drivers' Association of Australia and the Transport Workers Union say the ruling leaves workers open to continuing exploitation.
Experts have suggested Friday's ruling may not be the end of the matter and drivers could still take legal action against Uber.
"This finding is going to make things a lot harder for rideshare drivers in Australia," RSDAA secretary Les Johnson told AAP.
"These companies are now going to say we don't have to worry about (drivers) being classed as employees. It means that accountability has gone out the door."
Mr Johnson said "vulnerable" drivers could already be sacked without warning and without a right of reply.
The TWU says the ruling means drivers - who earn below minimum pay - are unable to negotiate wage increases, demand support when sick or receive superannuation.
But the union noted in May some 1700 Foodora riders received $2.3 million in back pay while in late 2018 a rider won an unfair dismissal case with TWU support.
The Fair Work Commission in November found Josh Klooger was an employee of the company, not a contractor.
"We know the same control factors are in play for workers in Uber and right across the gig economy," TWU national secretary Michael Kaine said in a statement on Friday.
UTS business school academic Sarah Kaine argued the ombudsman's Uber ruling was at odds with other jurisdictions such as the United Kingdom and "not decisive".
"I'd say we haven't seen the end to litigation," Associate Professor Kaine told ABC TV.
"Other organisations and individuals with a stake in the game will, I think, keep challenging (Uber)."