Mrs Williams played a key role in the hunt for justice for the 96 Liverpool fans, including her son Kevin, who died at Sheffield Wednesday's stadium in 1989.
She continued the fight over the last few months despite being terminally ill with cancer.
Last December, the original accidental death verdicts of the Hillsborough disaster inquests were quashed by the High Court and Home Secretary Theresa May announced a new police inquiry.
That move came after a damning report into the tragedy - which occurred in the early stages of an FA Cup semi-final against Nottingham Forest - revealed a cover-up which attempted to shift the blame on to the victims.
Medical evidence presented by the Hillsborough Independent Panel revealed that 58 of the victims "definitely or probably" could have survived beyond 3.15pm, the cut-off point imposed by the original coroner.
The original report had said that Kevin Williams and 94 other fans had died before 3.15pm but Mrs Williams consistently argued that claim, and even tracked down a witness who suggested Kevin uttered the word "Mum" at about 16:00.
Her calls for a fresh inquest were initially rejected by attorney generals and the European Court of Human Rights before the work of her and her fellow campaigners helped unearth such strong evidence that a new inquest was finally ordered.
Mrs Williams made her last public appearance on Monday at the annual Hillsborough memorial service at Liverpool's Anfield stadium.
The football club said on Twitter that the club "was saddened to hear of the death of [the] prominent Hillsborough campaigner Anne Williams."