Hundreds remember synagogue attack victims
The Chief Rabbi and Angela Rayner are among those at the event, nearly a year on from the attack.
Yoni Finlay, who was hit by a stray police bullet while helping to barricade the doors during the attack, will also speak at the service.
Earlier, asked by BBC Radio 4's Today programme about how the Jewish community in the UK feels almost a year on, he said: "I don't think things feel safer, I think we certainly live behind ever increasing gates, more security than we've ever had.
"Jewish people are having to hide their identity. Even my own son, who's in college at the moment, has faced death threats."
Other speakers at the memorial service include Alan Levy, who helped barricade the doors against the attacker, and Greater Manchester Police Chief Constable Sir Stephen Watson.
Although the first anniversary of the Heaton Park attack is not until October, the Jewish community will mark it on the religious anniversary rather than by the secular calendar.
The attack happened on Yom Kippur, the holiest day in the Jewish calendar, which falls in September this year.
Rabbi Walker said the service was being held because the community also wanted to hold a public memorial before the Jewish High Holy Days, both to ensure those affected are remembered by wider society and to call for change in society.
