Jagmeet Singh is the leader of Canada's federal New Democratic Party (NDP) as of the time of writing this question.
When Jagmeet Singh ceases to be leader of the federal NDP, who will replace him?
This question resolves to a named individual and not to “Other” or non-name answers. Acting or temporary leaders do not count. The resolution date will be extended as necessary until Jagmeet Singh is permanently replaced.
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The NDP has selected Don Davies as its interim leader - he will assist in running the party leadership convention (CBC).
Wikipedia has a page on the next NDP leadership race. I have added some of the names listed there as potential candidates.
Jagmeet Singh says "I'll be stepping down as party leader as soon as an interim leader can be appointed" (CBC).