1

Thranduil plays a big role in the events of The Hobbit, but he seems absent from the LOTR.

Does he play any part at all in the War of the Ring?

I've never read the books so I don't know if anything regarding Thranduil was left out of the movies.

2

As near as I can tell, Thranduil and his people (other than Legolas, obviously) only participated in one battle in the War of the Ring, when their home was invaded by the forces of Sauron.

From Appendix B: The Tale of Years:

In the North also there had been war and evil. The realm of Thranduil was invaded, and there was a long battle under the trees and great ruin of fire; but in the end Thranduil had the victory.

From a non-military perspective, they were also charged with keeping Gollum out of trouble. From The Fellowship of the Ring book 2, chapter 2 "The Council of Elrond" (emphasis mine):

'He is a small thing, you say, this Gollum? Small, but great in mischief. What became of him? To what doom did you put him?'

'He is in prison, but no worse,' said Aragorn, 'He had suffered much. There is no doubt that he was tormented, and the fear of Sauron lies black on his heart. Still I for one am glad that he is safely kept by the watchful Elves of Mirkwood.

Not the answer you're looking for? Browse other questions tagged or ask your own question.