There were laws, but the sum of them was "This is illegal", which I have discussed here. However, I suspect you more mean laws about how the duel was conducted, in which case we're talking about a mix of written (non-legal) codes and unwritten conventions which were broadly similar although varied some in time and place, which I have discussed here and here.

For further reading, I'd direct you here but of course can answer any follow-ups you might have.