What costs does a person owe if they discontinue a will challenge partway through in Ontario?

A person who discontinues an Ontario will challenge partway through generally becomes responsible for the other side's costs incurred up to that point, much as in other civil litigation, unless the parties agree otherwise or the court orders something different. The idea is that the estate (or another party) shouldn't be left covering the legal costs of defending a claim that the person bringing it ultimately chose not to pursue to a decision.

How much is actually owed, and whether it's reduced or waived, depends on the circumstances: how far the litigation had progressed, whether the discontinuance came promptly after new information came to light that reasonably changed the challenger's view of their case, and whether the original challenge had a reasonable basis in the first place. A challenger who discontinues quickly after receiving disclosure that undermines their concern is often treated more favourably on costs than one who discontinues only after running up significant costs on both sides. Because a request to discontinue can trigger a costs motion rather than simply ending things quietly, get advice on the likely costs exposure and how to approach the other side before discontinuing, rather than after.