Peter Demeter (born 19 April 1933) is a Hungarian-born Canadian former real estate developer convicted in 1974 of arranging the murder of his wife. It was the longest trial in Canadian history to that date, and revealed that both husband and wife may have been plotting to murder the other to collect a CA$1 million (equivalent to $6 million in 2023) insurance policy. The suspected contract killer Demeter hired was identified but never found.
While serving his sentence and living in a convicts' halfway house, in 1983 Demeter was charged on two counts with trying to arrange the kidnapping and murder of the son of his cousin; the latter was managing his financial affairs. In 1985 Demeter was convicted of the charges and given a second life sentence.