When first spoken to, Garevel will give the quest Last of the Legion.
Upon being informed that Amaranthine has lost most of its population after the darkspawn attack, he will suggest burning the city to prevent the remaining darkspawn from joining the army that is attacking Vigil's Keep. If the Warden refuses on the grounds that surviving citizens will be burnt, Garevel protests, but eventually defers to the Commander's judgement.
If you try to save the city, he will return at the end of the battle. He can be given discretion in what to do with the The Messenger, in which case he will release him (despite previously ordering his archers to shoot).
During The Siege of Vigil's Keep, he will guide the Warden-Commander to parts of the Keep which are under attack.
Captain Garevel is promoted to seneschal of Vigil's Keep after the events of Awakening. It is unknown what became of Varel in the cases where his death is not confirmed.If you import an Awakening character into The Golems of Amgarrak, you will receive a letter from him explaining the situation in Orzammar.