What is an affidavit of service and why do I need one in Ontario?

An affidavit of service is a sworn statement from the person who delivered legal documents, confirming who was served, what documents were served, when and how service happened, and where. It's the court's proof that the other side was properly notified of the lawsuit or a specific step in it, and it's generally required before you can take further action that depends on proper service having occurred — for example, noting a defendant in default, or asking the court to proceed with a motion the other side didn't respond to.

Without a filed affidavit of service, a court generally can't be confident that a defendant actually received notice, so steps requiring proof of service are usually blocked until it's on file. The affidavit is normally sworn by whoever actually performed the delivery, not the party who benefits from it, since it needs to reflect first-hand knowledge of what happened. Getting the details right matters: an affidavit that's vague about the date, method, or exactly who was served can be challenged later, potentially undermining steps that were taken based on it. Keeping careful notes at the time of service, rather than reconstructing details afterward, makes for a stronger affidavit.