Does a stepparent have to pay child support in British Columbia?

This answer covers the law of British Columbia.

Sometimes, but only in limited cases. Under the Family Law Act, a stepparent has a support duty only if they contributed to the child's support for at least one year and a proceeding is started within one year after their last contribution.

Even then, the duty is secondary to the duties of the parents and guardians, and it extends only as appropriate given the child's standard of living and how long the child lived with the stepparent. A stepparent is a spouse of the child's parent who lived with the parent and the child during the child's life, and an order against a stepparent requires a section 147(4) duty and that the stepparent and the parent are separated.

Guardianship is a separate question. A non-parent guardian's duty to support is secondary to that of the parents, and a new partner does not become a guardian only by marrying or entering a marriage-like relationship with a guardian. If a divorce is involved under the Divorce Act, a child of the marriage includes any child for whom both spouses or former spouses stand in the place of parents, and Guidelines section 5 then governs the amount. A lawyer can confirm how this applies to your family.