Ian Wilkinson, 68, and his wife Heather, 66, ate the meal at Erin Patterson's Leongatha home in the state's southeast on July 29.
Mrs Wilkinson died after the lunch, as did her sister Gail Patterson and brother-in-law Don Patterson, both 70.
The couple was honoured in a public memorial service last month, where their son Simon described them as being devout in their faith, but with humility rather than ignorance. Simon was also at Wednesday's service.
Mrs Wilkinson is being honoured in a service at the Korumburra Indoor Recreation Centre on Wednesday morning, with dozens of family members, friends and parishioners in attendance.
Mr Wilkinson was one of the many who trickled in for the service from about 10am.
The 68-year-old became critically unwell after the lunch, spending close to two months in the Austin Hospital.
The Baptist church pastor returned home on September 22, in what his family described as a "moment of immense relief".
They thanked the Korumburra community, church, friends, family, and colleagues for their support and prayers.
"This collective kindness has been a pillar of strength for Ian and the family, reinforcing the sense of unity and compassion that defines our community," the statement said.
Police believe the symptoms the four diners experienced were consistent with being poisoned by death cap mushrooms.
Erin Patterson is considered a suspect as she cooked the lunch that is believed to have led to the deaths.
She was interviewed by police and released without charge but has since faced intense media scrutiny.
In a statement to police, Ms Patterson said she made a beef Wellington using button mushrooms from a major supermarket and dried mushrooms bought at an Asian grocery store.
The 46-year-old said she ate a serving and later suffered bad stomach pains and diarrhoea, contrary to the suggestion of detectives that she did not fall ill.
Victoria Police have not commented on Ms Patterson's statement other than to say it was not one taken by officers, nor have they provided any updates on their investigation.