Like other Centaurs, Roonwit could read the stars, and foresaw terrible trouble about to come to Narnia.
He had read the stars, and said that Aslan had not in fact returned, but that something very sinister was afoot.
- "Never in all my days have I seen such terrible things written in the skies as there have been nightly since this year began. The stars say nothing of the coming of Aslan, nor of peace, nor of joy. I know by my art that there have not been such disastrous conjunctions of the planets for five hundred years. It was already in my mind to come and warn your Majesty that some great evil hangs over Narnia. But last night the rumour reached me that Aslan is abroad in Narnia. Sire, do not believe this tale. It cannot be. The stars never lie, but Men and Beasts do. If Aslan were really coming to Narnia the sky would have foretold it. If he were really come, all the most gracious stars would be assembled in his honour. It is all a lie."
- ―Roonwit (Chapter 2) [src]
After he had told Tirian this, a Dryad suddenly came to them, informing them of the Calormenes who were destroying their forests, and killing her and the rest of her kind, just before she too died.The king, in his anger, then sent Roonwit to Cair Paravel with his ring, as his token to raise an army against the Calormenes, when it became clear that they were under threat. Roonwit warned the king not to act so rashly, and suggested waiting a while first, but Tirian was adamant in his decision.
Roonwit was a loyal and obedient subject of the king, so he did as he was told, and left with the reinforcements to go to Cair Paravel.Alas, he was slain in the Cair Paravel Massacre when he was hit by Calormene arrows. His body was later seen by Farsight the Eagle.
- "And the other sight, five leagues nearer than Cair Paravel, was Roonwit the Centaur lying dead with a Calormere arrow in his side. I was with him in his last hour and he gave me this message to your Majesty: to remember that all worlds draw to an end and that noble death is a treasure which no one is too poor to buy."
- ―Farsight stating Roonwit's last words (Chapter 8) [src]
Afterwards, it was likely he was one of those who entered Aslan's Country, since he was among those most loyal to Aslan.