The regulatory system at Stafford Hospital was "wholly ineffective", a public inquiry heard.
Lawyers for Cure the NHS, a campaigning group made up of relatives whose family members died at the hospital, said the health system "completely failed".
The hearing is the fifth into the hundreds of higher than expected deaths at the hospital between 2005 and 2008.
Earlier inquiries into a 2009 report which condemned conditions at the hospital were heard in private.
The new coalition government ordered that an inquiry be held in public.
A Healthcare Commission report, issued in 2009, listed a catalogue of failings including receptionists assessing patients arriving at A&E, a shortage of nurses and senior doctors and pressure on staff to meet targets.
Jeremy Hyam, counsel for Cure the NHS, said: "The stark and worrying concern is that the regulatory system supposedly in place was wholly ineffective to prevent a dramatic lowering of standards not just for a matter of months, but for at least four years."
He asked how the hospital had managed to get Foundation Trust status, at a time when the care being given to patients was so poor it was capable of amounting to inhuman and degrading treatment under the European Convention on Human Rights.
"The inquiry is the culmination of more than three years of campaigning by members of Cure to expose the failings at Stafford Hospital," Mr Hyam said.
It was not just patient care which was failing but also the failure of the Mid-Staffordshire NHS Trust, and its supervisory bodies to prioritise patient safety over targets, he added.
Concluding his opening speech he said the inquiry was a chance to look at the regulation system within the NHS.
"The shocking experience of Mid Staffordshire suggests that despite the array of supervisory, regulatory and commissioning bodies within the health system, their individual and combine work completely failed... to maintain basic standards of care, dignity and respect for human rights," Mr Hyam said.
The inquiry was adjourned until Thursday.