He descended from the Númenórean noble house that settled in Belfalas by Elendil in the Second Age. Because of this, it is assumed he was an ancestor of Imrazôr, Galador and the Princes of Dol Amroth.
When King Ondoher led his army to face the Wainriders who threatened Gondor, Adrahil commanded the army's left wing. The soldiers of the right wing were under the command of the King's nephew Minohtar, while the centre was commanded by the king himself and his heir Artamir.
Ondoher's enterprise came to a devastating end: he was surprised by the Wainriders, and his forces were overwhelmed. Adrahil's soldiers, however, were shielded from the attack and survived it. Ondoher and Artamir had both been killed, and Minohtar took charge, sending Adrahil along with both his own command of the Left Wing and those at the rear of the Right Wing who had not yet been engaged.
Adrahil withdrew south into Ithilien to form a defensive line from Cair Andros to the Ephel Dúath. With these forces he was to cover the approaches of Minas Tirith and allow Minohtar to form a rearguard and attempt to stem the advance of the Wainriders. Adrahil should at once message Eärnil, and inform him of the disaster of the Morannon and of the position of the retreating Northern Army.
Adrahil's fate is uncertain; the Wainriders eventually broke through Minohtar's more northerly defence, but whether they penetrated to Adrahil's position is unknown. If he survived the initial assault, it seems likely that Adrahil would have joined with Eärnil in his counter-attack, seeing the ultimate defeat of the Wainriders at the Battle of the Camp.
Adrahil and the Princes of Dol Amroth
In the chapter Cirion and Eorl of Unfinished Tales Adrahil is referred to as "Adrahil of Dol Amroth". However, since Dol Amroth would not be named as such until after the drowning of Amroth in Third Age 1981 this must be an anachronistic error on the part of the chronicler.