Hammerwiki:Intelligence

Intelligence (Int) is a stat to represent a character's mental capacity and ability to reason. It is a measure of a character's ability to manipulate the Winds of Magic, and characters with higher intelligence will cause more damage and strike more critical hits with magical attacks, and will also have less chance of having their magical attacks disrupted by the enemy.

There are reports that Intelligence does not affect critical hit chance - Warhammer Alliance Forum Thread

1 point of int adds 0.088% to spell dmg.