The rule of spousal incompetency applies only where there is a valid and subsisting marriage. The rule does not apply to "common law" relationships or where the couple, although legally married, are irreconcilably separated.
In a civil case, any party or the spouse of any party is a competent and compellable witness for any party to the action.
In a criminal case, the spouse of an accused is a "competent" witness for the defence. The spouse of an accused is also a "competent and compellable" witness for the Crown where the accused is charged with offences listed in subsections 4(2) and 4(4) of the Canada Evidence Act. The spouse of an accused is also "competent" to testify for the Crown under the common law exception, which is preserved by section 4(5) of the Canada Evidence Act. The common law exceptions apply when: (1) the accused is charged with an offence involving the spouse’s person, health, or liberty; (2) even though there is no charge, evidence reveals that the accused threatened the spouse’s person, liberty, or health; or (3) violence, cruelty, or threats are made against the spouse’s child. There is an issue as to whether a spouse is "compellable" under common law; the preferred view is that the spouse on being found competent is also compellable.
At common law the parties and their spouses in a civil case and the accused and spouse in a criminal case were not competent to testify. This rule has been abolished in civil cases; parties and their spouses
are both competent and compellable to testify and, in fact, may well be called to do so by the opposing side. In criminal cases, under subsection 4(1) of the Canada Evidence Act, the accused and the spouse are made competent to testify for the defence. The accused may not be called to testify by the prosecution.27The spouse may, in certain circumstances, be called by the prosecution to give evidence. Subsections 4(2) and 4(4) of the Canada Evidence Act make the spouse "competent and compellable" to testify for the prosecution where the accused is charged with certain listed offences. Subsection 4(2) lists sexual of-fences and crimes against the marriage, such as polygamy (section 293). Subsection 4(4) is concerned with crimes that involve harm or violence to children. These lists are far from logical. For example, why may the spouse be called to testify where the victim of a murder is under fourteen years of age, but may not testify when the victim is over the age of fourteen? The enactment of these sections indicates a trend towards the erosion of spousal incompetency.
This trend is also evident in the common law exception, which is preserved in subsection 4(5) of the Canada Evidence Act. At common law the spouse could testify in cases that involved the spouse’s "person, liberty, or health." Obviously, if spouses were not allowed to testify they could well be victimized in secret with complete immunity.28The exception applies, however, even when the spouse is not the "charged" victim. In R. v. Schell the accused was charged with first degree murder in an alleged contract killing.29The Crown sought to call his estranged spouse to testify as to a conversation in which the accused admitted to the killing. The accused had also told his wife that if she said anything she or her children could be shot. The court found it absurd to confine the common law "threat" exception to situations where the accused is actually charged with the threat against the spouse. No useful purpose is served. Surely once such a threat is made there is little marital harmony to preserve and there is every need to provide protection to the spouse. For similar reasons this exception has been expanded to include crimes of violence or threats of violence against the spouse’s children.30At common law and under statute, the rule applies...