Pandy said the missing relatives were in Hungary
His daughter is to be jailed for 21 years.
Andras Pandy, 74, had been found guilty of murdering two of his wives and four of his children, as well as raping three of his daughters.
As well as being a co-defendant, his daughter Agnes, 44, was the chief prosecution witness against him. She was found guilty of helping her father carry out four of the murders, even though her lawyers claimed she was under her father's "irresistible spell".
Pandy, who spent much of the trial smiling, had always denied the charges, claiming the family members were still alive in Hungary.
The bodies have never been recovered. Prosecutors say they were cut up with knives and dissolved in drain cleaner.
Police criticised
The pastor, who came to Belgium as a refugee in 1957 and set up a Hungarian Protestant church in the Flemish part of the country, is also suspected by police of killing other people whose remains were reportedly found in three of Mr Pandy's homes.
The six missing members of the Pandy family disappeared between 1986 and 1990. Police were originally satisfied with Mr Pandy's claims that they had gone to live abroad.
The prosecution alleged that he killed them to cover up his sexual relationship with his step-daughter,Timea, after she became pregnant with his child.
Shortly afterwards she fled to Canada with her son.
Agnes said that she and her father made several trips to Canada in an attempt to find Timea, kill her, and recover her now 16-year-old son.
Belgian police have been criticised for their handling of the investigation.
They are still under heavy scrutiny following the case of Marc Dutroux, who is due to stand trial for the kidnap and murder of four girls aged between eight and 19.
The case only came to light after national outrage over the Dutroux saga forced police to re-examine old allegations of child abuse.