For the most part, the narrator of Sir Gawain recounts his tale in a third-person voice limited to Gawain’s point of view. This voice is necessary in order for the tale’s surprise ending – that Sir Bertilak and the Green Knight are really one and the same person – to really be a surprise.
There are a few exceptions to this narrative voice, however. One occurs at the start of the tale, where the narrator begins by setting the tale after "the siege and the assault were ended at Troy," when King Arthur rules the land (1). Although the narrative voice is still third person, it’s not from Gawain’s point of view; we haven’t met him yet. Also, when Sir Bertilak goes hunting, the narration follows all the action like he’s hovering in the sky among the displaced animals and their pursuers, watching them fall into the hunters’ nets.
In the first section of the tale, the narrator begins a technique he continues throughout the poem, of referring to his story as one he’s heard told before, or read in a book: "If you will listen to this story just a little while / I will tell it once, as I heard it told" (30-31). At these moments, the narrative voice shifts to first person as we’re caught up in the fiction of being in the same room with our storyteller, listening as he recounts a legendary, well-known story. These kinds of moments are peppered throughout the narrative; for example, when the narrator tells us to "be quiet a short while, / and I’ll tell how things turn out" (1996-1997). The effect of these insertions of the narrator’s own point of view is that we never forget that we’re hearing this story through the filter of our narrator.