How do I bring a motion to add or remove a party from a lawsuit in Ontario?

If a lawsuit is missing someone who should be involved, or names someone who shouldn't be, a party can bring a motion asking the court to add, remove, or substitute a party. Courts generally allow adding a party where it's necessary to properly determine the real issues in the case — for example, a person whose involvement in the underlying events makes them a necessary party to resolve the dispute fully, or a company that was named incorrectly and needs to be corrected. Removing a party is typically appropriate where someone has no real connection to the claims being made, or where continuing to include them serves no purpose but added cost and complexity.

The motion is usually supported by an affidavit explaining why the change is needed and what role the party being added or removed plays in the dispute. Courts are generally more willing to grant this kind of amendment earlier in a case, before significant steps have been taken, and more cautious later, especially if adding a party would effectively let a plaintiff sue someone new after a limitation period has expired. Existing parties are normally given a chance to respond before the change is made, since adding or removing someone can affect everyone already in the case.