Can an adult sibling who was financially dependent on the deceased bring a dependant support claim in Ontario?

Yes — a sibling can qualify as a "dependant" under Part V of the Succession Law Reform Act, but only if they meet the same core test that applies to any dependant: the deceased was supporting them, or was under a legal obligation to support them, immediately before death. Being related as a sibling isn't enough on its own; what matters is the actual support relationship, not the family label.

In practice, this means an adult sibling who can show the deceased was providing regular financial support — covering housing costs, paying bills, or otherwise being relied on for day-to-day needs — has a real basis to bring a claim if the will, or intestacy, leaves them without adequate provision. A sibling who wasn't actually being supported won't qualify just because of the relationship, even if they were close to the deceased or in financial difficulty generally. As with all dependant support claims, timing matters too: the claim must generally be brought within six months of the estate certificate being granted, though a court has some discretion to allow a later claim against any part of the estate not yet distributed. Anyone in this situation should gather evidence of the actual support relationship early and get advice promptly.