Editorial: In Dishonored
is Corvo Emily's father?
This is another theory editorial, but unlike the last one, this editorial actually has a pretty straightforward answer, and that answer is yes. I mean, if you missed that in the first game, between the two playing hide and seek together, Emily's obvious familial affection for Corvo, and the drawing of him with 'DADDY' written on it, then I'm honestly not sure what to tell you apart from reassuring you that, yes, Corvo does meet the requirements for being Emily's father.
Really, this editorial should be titled 'In Dishonored, is Corvo Emily's biological father in addition to being Emily's actual father', but that's a very long editorial title.
Again, though, we find that this question as a pretty straightforward answer, and that answer is 'it seems likely.' After all, while Corvo is hardly an absentee father - he's a very present and devoted one - any kind of official relationship between him and Jessamine would compromise her authority.
As an empress in a patriarchal society, openly being in a relationship with her own protector would, apart from quite possibly being scandalous, bring with it pressures for her to get married and to thus relinquish her monarchal power to Corvo. Jessamine shows no desire not to rule, but even if she did, becoming consort to an emperor would be the worst of both worlds, requiring that she give up her birthright and power to a man who has never ruled in his life, while still having to deal with the pressures and expectations of an empress. That's no way to live.
Neither does Corvo give any suggestion of wanting or being able to rule. Granted, as a silent protagonist, he rarely gives any suggestion of anything, but it's worth noting that there are no endings in which he isn't dutifully supporting Emily's rule without trying to rule through her - even in an ending where Corvo's as bloodthirsty and evil as they come, he's bloodthirsty and evil with no interest in running a country.
Not to mention, the man has been Lord Protector since he was a child. He's found his niche in life, and it's lord protectoring.
So that's their motivation covered, and we actually know that Corvo and Jessamine had a secret relationship: According to the Dunwall Archives, they started their affair in the Month of Rain of 1823, five years before Emily is born. That in and of itself is pretty clear evidence: If Corvo and Jessamine had a monogamous relationship and Jessamine was never unfaithful to Corvo - and there's nothing to suggest she was or would be - then Corvo is literally the only candidate for Emily's father.
Equally clear is that Emily believes that Corvo is her biological father. Granted, as a seven year old girl, she is maybe not the best authority on such things, but we do find research materials in her room about the Fugue Feast, a festival taking place at the end of the year, during a period of time which is deemed 'not to exist' by the authorities of Dunwall, making any acts committed during that period effectively not exist.
What a useful time that would be for Emily to be conceived. After all, even if Corvo and Jessamine had literally conceived her in public, people wouldn't be able to acknowledge that they had. Emily would, in the eyes of the law and everyone else, be immaculately conceived.
So there you have it. Is Corvo Emily's father? Yes. Is he her biological father? Almost certainly still yes. Marvelous.