11. Any person charged with an offence has the right:
g. not to be found guilty on account of any act or omission unless, at the time of the act or omission, it constituted an offence under Canadian or international law or was criminal according to the general principles of law recognized by the community of nations;
Similar provisions may be found in the following Canadian laws and international instruments binding on Canada: article 15(1) of the International Covenant on Civil and Political Rights.
See also the following international, regional and comparative law instruments that are not legally binding on Canada, but include Similar provisions: article 9 of the American Convention on Human Rights; article 7(1) of the European Convention for the Protection of Human Rights and Fundamental Freedoms; and article 1, sections 9 and 10 of the United States Constitution, which prohibits the Congress and States from passing any ex post facto law.
The other explicit Charter right against retrograde temporal application is paragraph 11(i), which provides the benefit of the lesser punishment if the punishment for an offence has been varied between the time of commission and the time of sentencing. The Supreme Court also has interpreted paragraph 11(h) of the Charter (double jeopardy) as providing restrictions against retrospective changes to the conditions of the original sanction that have the effect of adding to the punishment received (Canada (Attorney General) v. Whaling,  1 S.C.R. 392).
Residual rights in respect of the retroactive or retrospective application of law may apply under section 7 of the Charter in situations where life, liberty or security of the person is at stake (R. v. Gamble,  2 S.C.R. 595; Cunningham v. Canada,  2 S.C.R. 143).
There also exist common law interpretive presumptions against retrospective and retroactive operation of statutes and against interference with vested rights. These presumptions, however, are of varying weight and, unlike the constitutional restrictions, can be displaced by explicit terms of legislation or by the necessary implication of its provisions. Subject to the restrictions in the Charter, there is no general constitutional restriction against legislative retrospectivity or retroactivity (British Columbia v. Imperial Tobacco Canada Ltd.,  2 S.C.R. 473).
While analyzing the separate issue of vagueness in law, and not commenting directly on paragraph 11(g), the Supreme Court has alluded to principles against retroactivity in criminal law as being related to the ancient Latin maxim nullum crimen sine lege, nulla poena sine lege: no crime without law, no punishment without law. The Court referred to the underlying purpose as being to ensure that citizens are able to foresee the consequences of their conduct so as to be given fair notice of what to avoid, and to limit the penal law discretion of the state (Lamer J. in a concurring opinion in Reference re section 193 and paragraph 195.1(1)(c) of the Criminal Code,  1 S.C.R. 1123 at paragraph 34 cited by the Court as a whole in R. v. Levkovic,  2 S.C.R. 204 at paragraph 2). This expression of purpose has been directly linked to paragraph 11(g) in Front commun des personnes assistées sociales du Québec v. Canada (Canadian Radio-Television and Telecommunications Commission), 2003 FCA 394.
There is relatively little jurisprudence providing detailed consideration of paragraph 11(g) of the Charter. Issues related to retroactive offences requiring examination under paragraph 11(g) appear to arise infrequently in comparison to issues related to temporal application of changes in punishment analyzed under paragraph 11(i) or paragraph 11(h).
A leading case is R. v. Finta,  1 S.C.R. 701. In that matter, changes to the Criminal Code, through the enactment of subsection 7(3.71) that extended Canadian territorial jurisdiction over war crimes and crimes against humanity, were challenged under, inter alia, paragraph 11(g) of the Charter (N.B., an analogous extension of Canadian jurisdiction is now provided by section 8 of the Crimes Against Humanity and War Crimes Act, S.C. 2000, c. 24). Six of the seven justices hearing the case addressed the paragraph 11(g) issue, but they were divided on the issue The three Supreme Court justices who formed the majority for the judgement on the whole found that the new provisions effectively created new offences in Canadian law that were retroactive in nature. These three found, however, that there existed an exception in the principles of fundamental justice that allowed for retroactive application of offence provisions for acts of this nature, which were illegal and immoral, even if they were not punishable by specific offence provisions when they were committed. The reasons were stated more in terms of section 7 of the Charter than paragraph 11(g), but ostensibly resolved the paragraph 11(g) issue as well. Three other justices, dissenting in part on the judgement on the whole, found that the new provisions were jurisdictional in nature and did not create new crimes: the offences charged were contrary to Canadian and international law at the time they were committed and so did not facially violate paragraph 11(g). In any event, these three justices viewed any violation of paragraph 11(g) to be precluded, as the terms of the Charter provision allowed for conviction for offences under international law and for acts which are criminal under general principles of law recognized by the community of nations: these stipulations were included in paragraph 11(g) to allow for prosecution of war crimes and crimes against humanity.
The Supreme Court has ruled that paragraph 11(g) is not concerned with whether a criminal law was published, but only with whether the law provided that the impugned conduct was criminal at the time of its commission (R. v. Furtney,  3 S.C.R. 89). This does not necessarily mean that some concept of availability of the law is not constitutionally protected under the Charter, perhaps as an extension of a fair notice requirement that is part of the nullum crimen principle referred to elsewhere by the Supreme Court (see above). Stevenson J. in Furtney seemingly kept open the potential for some Charter protection for a principle of availability of the law, at paragraph 46, while ruling that such a principle was not violated in that case.
The fact that an offence exists at common law and is not codified (i.e., criminal contempt) does not result in a breach of paragraph 11(g) (United Nurses of Alberta v. Alberta (Attorney General.),  1 S.C.R. 901).
There has been some jurisprudential analysis of whether a retroactive restriction of a defence would violate paragraph 11(g) of the Charter. A lower court has ruled that a retroactive limitation of a defence would violate paragraph 11(g) as it would have the effect of retroactively extending the circumstances to which criminal liability will attach (R. v. Carriere, 2013 ABQB 645). Comments made by the Ontario Court of Appeal suggest agreement with this perspective, albeit the comments were briefly stated and the Court of Appeal did not have to decide the issue (R. v. Bengy, 2015 ONCA 397 at paragraphs 64-65). The Supreme Court of Canada has employed interpretive principles of temporal application in ruling against a legislative interpretation that would allow for a retrospective limitation of a defence (R. v. Dineley,  3 S.C.R. 272).
The Federal Court of Appeal has taken into consideration paragraph 11(g) of the Charter in ruling against the retroactive insertion of a condition into provisions of a regulatory statute. The Court of Appeal noted that since violation of the regulatory provisions also was made an offence under the statute, retroactive insertion of the condition would violate paragraph 11(g) (Front Commun, supra).
An appellate ruling indicates that paragraph 11(g) does not preclude reliance on evidence that pre-dates the time that an offence came into existence in law. This ruling suggests that provided that the act or omission for which conviction is obtained itself took place in the period during which an offence existed, evidence from an earlier period, prior to the coming into force of the offence, that helps to establish the context of the alleged criminal activity, and that may help to prove the offence, may be admitted without violating paragraph 11(g) (R. v. Ryback (1996), 105 C.C.C. (3d) 240 (B.C.C.A.)).
A lower court decision held that a conviction for the offence of laundering proceeds of crime does not violate paragraph 11(g) even if the conviction pertains to the laundering of proceeds of criminal activities that themselves pre-dated the coming into force of the laundering offence. Provided that the proceeds were the product of activities that were criminal when they were committed, and providing the act of laundering itself took place after the laundering offence was created in law, no violation of paragraph 11(g) arises (R. c. Flahiff,  R.J.Q. 626 (Cour du Québec), referring also to Les Entreprises Michel Chouinard Inc. v. Canada (Attorney General), (unreported, Nov. 18, 1992, Quebec S.C.)).