What Makes a Marriage Valid — or Void — in Ontario?

Most people assume that once they've had the ceremony and signed the paperwork, their marriage is legal and that's that. But Ontario's Marriage Act and common law establish specific requirements that must be met for a marriage to be valid — and when they aren't, the marriage may be void (never legally existed) or voidable (legally defective and subject to being set aside). Understanding the difference matters if you're questioning whether a marriage was legally effective, dealing with a prior undisclosed marriage, or considering annulment rather than divorce.

Requirements for a Valid Marriage in Ontario

Under Ontario's Marriage Act and federal common law, a valid marriage requires:

1. Capacity

Both parties must have legal capacity to marry. This means:

• Age: Both parties must be at least 18 years old. Minors under 18 cannot marry in Ontario; there is no longer any provision for underage marriage with parental or court consent (this was changed by federal legislation).
• Mental capacity: Both parties must understand the nature of the marriage contract at the time of the ceremony. A person who lacked mental capacity due to illness, medication, intoxication, or other cause at the time of the ceremony did not validly marry.
• Not already married: Both parties must be unmarried. This means legally divorced, widowed, or never married. A person who goes through a second marriage ceremony while still legally married to someone else has committed bigamy — and the second "marriage" is void.

2. No Prohibited Degrees of Consanguinity

Ontario prohibits marriage between closely related family members. The Marriage (Prohibited Degrees) Act (federal) defines the prohibited degrees of consanguinity and affinity. Generally, direct ancestors and descendants (parent-child, grandparent-grandchild) and siblings are prohibited, regardless of whether the relationship is biological or adoptive.

3. Genuine Consent

Both parties must freely and genuinely consent to marry each other. Consent obtained through:

• Fraud or misrepresentation (e.g., false identity or concealment of a fundamental fact)
• Duress (threats or coercion)
• Mistake (e.g., mistaken identity)

may render the marriage voidable.

4. Proper Ceremony

The marriage must be solemnized by a person authorized to perform marriages in Ontario — a licenced officiant, a judge, a justice of the peace, or a religious official registered under the Marriage Act. The ceremony must include the prescribed declaration of consent in the presence of at least two witnesses.

5. Marriage Licence or Publication of Banns

Before the ceremony, the parties must have either a marriage licence (issued by a municipal clerk in Ontario) or have gone through the publication of banns process (typically used in religious ceremonies). Proceeding without either is a defect, though courts have discretion on whether it voids the marriage.

Void Marriages: Never Legally Existed

A void marriage is one that has no legal effect from the start — it is treated as if it never happened. No court order is required to make it void; the void status exists automatically. However, obtaining a court declaration that the marriage is void provides important clarity and documentation.

Grounds that make a marriage void in Ontario include:

• One party was already married at the time (bigamy)
• The parties were within a prohibited degree of relationship
• Either party was under 18 at the time of the ceremony

Because a void marriage has no legal existence, the parties cannot obtain a divorce — there is nothing to divorce from. They typically apply for a declaration of nullity to formally confirm the marriage's non-existence, particularly if they need documentation for a later marriage or for property/estate purposes.

Voidable Marriages: Valid Until Set Aside

A voidable marriage is legally valid and subsisting until a court declares it void. Unlike a void marriage, a voidable marriage requires a positive court order — a decree of nullity — to be undone. If neither party seeks to set it aside, the marriage continues as a legal marriage.

Grounds that may make a marriage voidable include:

• Lack of genuine consent (duress, fraud, or misrepresentation about something fundamental)
• Mental incapacity at the time of the ceremony (where this doesn't rise to the level of making the marriage void outright)
• Inability to consummate the marriage (in limited circumstances recognized by courts)

A decree of nullity has retroactive effect — it declares the marriage never to have been valid. This matters for property rights, inheritance, spousal support, and the ability to remarry without going through divorce proceedings.

Annulment vs. Divorce: The Practical Difference

• Divorce ends a valid marriage. You must have been legally married and must meet the grounds for divorce under the Divorce Act (most commonly, separation of at least one year).
• Annulment (nullity) is a declaration that the marriage was never valid. There is no separation-period requirement, but you must establish valid grounds for nullity.

From a practical standpoint, most people who want to end their marriage will seek a divorce rather than an annulment, because the grounds for annulment are narrow. However, if there is a genuine question about whether the marriage was valid at all, a declaration of nullity may be appropriate.

Note that religious annulments (granted by churches) are entirely separate from legal annulments and have no effect on civil law.

Property Rights in Void and Voidable Marriages

This is an area where things get complicated. Ontario's Family Law Act property regime — which divides the value of property accumulated during marriage — applies to legally married spouses. If a marriage is declared void from the start, the Family Law Act may not apply in the same way it would to a valid marriage, and the court may need to apply equitable principles (like unjust enrichment) to divide property fairly.

If you are dealing with a void or voidable marriage situation, obtaining legal advice before taking any steps is strongly recommended.

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