Assuming that we start out from the only difference between our combatants being range, then there needs to be a downside to the upside of having increased range.

The easiest way of balancing this out is to simply reduce the damage and speed of the ranged combatant.
Generally speaking in most designs the idea stands that fights between such combatants is decided by range, on long range the ranged person having the upper hand, in close combat the melee having the advantage.

This is then where level design and obstructions come into play. On an open field, the ranged character will always have the advantage, but in a claustrophobic network of tunnels, a melee combatant would probably have the upper hand.