

It is definitely atypical for the PM not to be a sitting MP, but it is within the confines of the constitution. The PM only needs to be elected by and then maintain the confidence of parliament.
It’s almost certain that he will call an election immediately, however. A non sitting PM won’t maintain parliamentary confidence for long.
Or a Liberal MP in a safe seat will resign and Carney will stand in the subsequent by-election.
The Americans need to learn from the French where one egg is un oeuf.