Earlier, the city observed a two-minute silence at 3.06pm - the time the FA Cup semi-final was abandoned - as the bells at Liverpool Town Hall and other civic buildings rang out 96 times.
The silence was also observed at Liverpool Cathedral as a press conference was being given by the families.
Tonight's vigil, organised by the city council, was taking place at Liverpool's St George's Hall.
Speaking before the vigil got under way the city's executive mayor, Joe Anderson said: "This is a momentous day that the families and the city have waited 23 years for.
"It is absolutely clear for everyone to see that those affected were victims not only of a terrible event, but also of an unforgivable miscarriage of justice. They were aided and abetted by some sections of the media, who should now apologise for misleading the nation and smearing the reputation of Liverpool FC fans and the city.
"It is to the credit of families that they have never given up on their quest to find out what happened on that dreadful day.
"Now that we finally have the truth of what happened in 1989, we must make sure the families get the justice they deserve. I am calling on the Attorney General to apply to the High Court immediately to quash the original inquest verdicts so that a fresh inquiry can be held.
"Furthermore, those who played a role in the cover-up should be brought to account for their deceit and corruption. The people of Liverpool will stand shoulder to shoulder with the families as we seek to make sure they get justice they have sought for so long.
"We will never forget the impact the Hillsborough disaster had on the bereaved families, on the lives of those who were caught up in the disaster and the long journey the entire city has had to endure for the truth to be heard."
Flags at council properties have been flown at half mast throughout the day in memory of the 96.