Do I have to look for a new job while I'm suing my former employer for wrongful dismissal in Ontario?

Yes. A dismissed employee generally has a duty to make reasonable efforts to find comparable new employment during the notice period, rather than simply waiting out the notice period without looking for work. This is called the duty to mitigate damages, and failing to make reasonable efforts can reduce the amount a court ultimately awards, since the purpose of wrongful dismissal damages is to compensate for actual income loss during the notice period, not to guarantee a fixed payout regardless of effort.

What counts as reasonable effort depends on the circumstances - your field, seniority, and the local job market - and you are not required to accept a job that is significantly worse in status, pay, or working conditions than the one you lost. If you do find comparable work before the notice period ends, the income earned generally reduces what your former employer owes for the remaining part of that period, since you are being compensated for actual loss rather than a guaranteed windfall. Keeping records of your job search efforts - applications, interviews, and dates - is useful evidence if the adequacy of your mitigation efforts is ever disputed in negotiations or in court.