Can a limited partner in an Ontario limited partnership take part in managing the business?

Not without risk. The whole basis of a limited partner's capped liability under Ontario's Limited Partnerships Act is that they stay in the position of a passive investor and leave control of the business to the general partner. If a limited partner takes part in managing or controlling the business — beyond exercising the kinds of oversight a passive investor is generally permitted, such as voting on fundamental changes to the partnership — they risk losing their limited-liability protection and being treated as though they were a general partner for that involvement.

This is a fact-specific test rather than a bright-line rule, and it catches limited partners who genuinely didn't realize their level of involvement had crossed a line — getting too hands-on with day-to-day decisions, directing operations, or acting outwardly as though they run the business can all be risky even if the limited partnership agreement still labels them a limited partner. If you're a limited partner who wants to be more actively involved than a purely passive investor, get legal advice on what oversight you can safely exercise under the agreement and the statute before doing so, since the consequences of getting it wrong are significant.