The carers are concerned about their lack of employment rights, not being listened to when a child is removed from their care and rates of pay.
Their vote at a meeting in Parliament on Monday was supported by shadow chancellor John McDonnell.
The Department for Education said it was launching a fundamental review of fostering across the country.
Foster carers can be employed by private agencies but the majority are given work by local authorities.
There are around 55,000 fostering households in the UK which care for some 64,000 children.
Foster carers are paid an "allowance" to cover the cost of the child in their care and a "fee" based on their skill level and time.
Weekly sums for an individual child can range from Â£150 to Â£500, depending on factors such as how demanding the child is.
But some foster carers are deeply unhappy about the way they are treated.
On Monday 60 current and former carers met in a crowded committee room in Parliament to share their experiences and to take the unprecedented step of voting on whether to unionise.
At the heart of their concerns is their legal status.
They are not classed as employees or workers, because they are not engaged under a contract of employment.
This means that they are not entitled to any of the rights enjoyed by employees or workers such as sick pay, holiday pay, or the national minimum wage.  '
"I don't know anyone else who works and doesn't get a pension, sick pay, holiday pay, or recognition as a professional," one of the foster carers said.
Foster caring can be hugely rewarding and fantastically challenging.
Nicola - not her real name - together with her partner has fostered more than 140 children.
Some have stayed with her family for a night or two, others for years.
The majority have been troubled teenagers.
"We had one occasion when a young person in a very high state of distress stabbed a door repeatedly in our home numerous times.
"And following another incident I had to run down the street I was so scared.
"We've had lots of times when we've had to leave our home and ask for police assistance to re-enter," she says.
However, Nicola, along with other foster carers, loves the work, especially when troubled children are able to re-enter education.
With pride and pleasure Nicola talks of how one of the children she fostered who has turned her life around is applying to university and remains in close touch.
Another concern at the meeting was the right to due process.
Many foster care workers have complained that children can be removed from their care without their input or consultation.
They claim there is little redress for them in cases of unfair and inappropriate removals.
They are sometimes excluded from the discussion about removal of the child, or removal is based on accusations against the foster carer which he or she is not allowed to defend.
The complaint about lack of due process also applies to decisions of local authorities to "de-register" foster care workers, meaning that they will no longer receive any placements from that local authority.
Some foster care workers told the BBC it is very difficult to become registered with another local authority or private agency.
They claim that de-registration can serve as a sort of black-listing.
The Department for Education points out that national minimum standards make clear that investigations into allegations or suspicions of harm should be handled fairly, quickly, and consistently in a way that protects the child, and supports the person who is subject to the allegation.
In addition, foster carers whose approval is terminated or terms of approval are amended have the right to a review by the independent review mechanism
Shadow chancellor John McDonnell, who attended the meeting to support unionising, said: "Foster caring is an essential role in our society, and these foster carers carry a burden for the rest of our community so they should be properly recognised.
"They have never really been recognised and had legal rights. They should have security of their employment and be properly paid as well, and they should have the support that they need."
The meeting was organised by the Independent Workers Union of Great Britain, a small trade union which has previously unionised low paid migrant workers in London.
Once the discussion was over the union asked the foster carers to vote.
Fifty-six hands shot into the air and a moment of history was made.
They benefit from the highest level of employment protection. There must be a contract between the employee and employer requiring the employee to carry out duties personally, meaning they cannot send someone else to carry out their work.
The employee must also be under the control of the employer in terms of hours, working practices and workplace rules, and be sufficiently integrated into the workplace.
Rights and benefits include holiday pay, national minimum wage, rest breaks, discrimination protection, whistleblowing, deduction from wages, pension contribution from an employer under auto-enrolment, a written contract of employment, unfair dismissal protection, redundancy payment, statutory minimum notice pay, maternity/paternity pay, paid time off for antenatal appointments and a right to request flexible working.
They hold an intermediate position between employees and the self-employed. There must be a contract between the worker and employer requiring the worker to carry out duties personally but the worker is not integrated or subject to as much control as an employee.
If the "employer" is actually a client or customer of any business carried on by the individual, they will not be a worker, but will instead be self-employed.
Rights and benefits include holiday pay, national minimum wage, rest breaks, discrimination protection, whistleblowing, deduction from wages and pension contribution from employer under auto-enrolment.
This status carries the least legal protection. There will be a contract but there is no requirement that the self-employed worker carries out the service personally.
The self-employed usually enjoy maximum freedom as to how to deliver the service and are not subject to workplace rules. Rights tend to be governed by the contract rather than any statutory rights.
Source: Cloisters barristers chambers
Individual foster carers have joined unions in the past, but no group has ever voted to form its own.
Although this may be a very small number, Dr Jason Moyer-Lee, the general secretary of the Independent Workers Union of Great Britain, believes the vote will mark a real change.
He said: "People who work in foster care, alongside social workers, local authority employees, and others, together form part of a professional network responsible for looking after some of society's most vulnerable individuals.
"Foster care work is important, demanding, and all too often highly exploitative. Like social workers and others who work in care, foster care workers should be remunerated properly, treated fairly, and have recourse to due process. By voting to unionise this is precisely what they aim to achieve."
A Department for Education spokesperson said:  "We really appreciate the work foster carers do, as we know it is a very rewarding, but at times challenging, experience.
"Foster carers receive financial support to cover the full cost of caring for a child and we're launching a fundamental review of fostering across the country, which will look at the issues affecting foster carers, including accountability and complaints."
A group of foster care workers have voted to form the first ever trade union for the profession.