Depending on the jurisdiction in which the case is tried, a defendant receiving a life sentence may become eligible for parole after serving a minimum length of time, on the order of 15–25 years.
The mandatory penalty for first-degree murder is life imprisonment with 25 years' ineligibility for parole.
Section 745.51 was found to be unconstitutional by the Quebec Superior Court and Quebec Court of Appeal in the case of Alexandre Bissonnette; and the Supreme Court of Canada dismissed the Crown's appeal in May 2022, finding multiple periods of parole ineligibility for first degree murder to be unconstitutional due to imposing an in effect irrevocable life sentence, contrary to the function of parole after a minimum period, which would be "grossly disproportionate" punishment and thus contrary to the Canadian Charter of Rights and Freedoms.
[5] The Supreme Court of Canada's declaration of constitutional invalidity meant that section 745.51 was struck down retroactively.
The result of the case law is hence that, per the law prior to 2011, that the sole penalty for murder is life imprisonment with 25 years' ineligibility for parole, regardless of how many murders are committed; in effect, only the plausibility of being granted parole is affected.