I am a 5th level fighter with an extra attack and I have TWF and the Dual Wielder feat.
In theory, could I use my first two attacks with a greatsword and then make a bonus action attack with a longsword on one turn, without being required to use my bonus action to unsheathe my longsword and waiting for a new turn to attack again?
I read that I would only need two hands to use the greatsword, not just to hold it.
So again, in theory, could I attack twice with a greatsword and use a free action to unsheathe my longsword with the Dual Wielder feat, and use my bonus action to attack with the longsword in one turn?
Best Answer
You need to be holding both weapons when you Attack in order to use Two-Weapon Fighting - and attacking with a greatsword requires both hands.
You have the Dual Wielder feat, so it doesn't matter that neither weapon is light. So far so good, however:
The Two-Weapon Fighting rules state:
There are two problems here.
Firstly, and most simply, when you attack with a greatsword you are not 'holding [it] in one hand' - it's true that you can hold a greatsword in one hand - but not while you're actually attacking.
Secondly, while it's not completely explicit, TWF is generally understood to require that you must already be holding both weapons, when you take the Attack action with the first weapon, in order to have the option of Bonus Action attacking with the second weapon. For evidence of consensus on this ruling elsewhere, see these other related questions, here and here.
To attack with your greatsword you need to use both of your hands, not one hand, and you can't be holding your longsword in the 'other hand' while doing it. You therefore don't meet the requirements of the two weapon fighting bonus action.