Which is correct: "confirm with somebody" or "confirm to somebody"?

Solution 1:

With is correct:

I'd like to confirm with you that you will finish the report by Thursday.

You can also request confirmation:

Please confirm that you'll finish the report by then.
I need your confirmation that you'll do it on time.

With this sense, you can also confirm something for someone:

Let me look at my calendar to confirm that for you.

That is, to act on their request for confirmation.

Solution 2:

I think there are three distinct meanings for "confirm":

• "get confirmation from"

• "give confirmation to"

• "mutually reach a firm agreement from some more vague state"

I think all of them can use "with" (which can therefore sometimes be ambiguous). The second can also use "to".