I am employed in the US but not a US citizen. My uncle, who is not a US citizen either and lives overseas, would like to gift me money by sending it as a wire transfer from he's account overseas to mine in the US. Assuming the amount is between US $500K - $1M, what would be my IRS Tax filing/declaration requirements if any? Would I have to actually pay any taxes?

NO taxes will be due, but the transaction will need to be reported on Form 3520.