Madhavan and Vijay Sethupathi met for the 1st time on the sets of Vikram Vedha. It was a deliberate move to retain the play between them on their very first interaction scene.
More than 3000 bullets (blanks, specifically used for cinema) were fired on the sets.
Madhavan's character Vikram shoots twice for every kill; that's his signature style.
When characters are introduced, Vikram is wearing a white shirt (portraying Good), while Vedha is wearing a black shirt (portraying Evil). However by the end of the movie, both characters are in grey shirts (portraying their respective journey towards the grey zone in between Good and Evil).
The guns used by the cops in the film are authentic pistols issued to Tamil Nadu police force.