Can a defendant challenge whether they were properly served in Ontario?

Yes — a defendant who believes they weren't properly served can bring a motion challenging the validity of service, rather than simply ignoring the lawsuit and hoping it goes away. This is an important option, because ignoring a claim you believe was improperly served can still lead to being noted in default if you don't respond, leaving you to argue about service after the fact instead of before. The motion typically argues that the method used didn't comply with the applicable rules — for example, documents left with the wrong person, delivered to an outdated address, or a defendant who was never actually notified despite the plaintiff's claimed method of service.

The court examines the evidence about how service was actually carried out, generally set out in the affidavit of service, against what the defendant says actually happened. If the challenge succeeds, the court can set aside any steps taken based on the defective service, such as a default judgment, and require the plaintiff to properly serve the defendant before the case continues. Because these challenges are fact-specific and timing matters, a defendant with real doubts about whether they were properly served should generally raise the issue promptly rather than waiting, since delay can weaken the argument that the defect caused genuine unfairness.