"Live Forever" is in the key of G major (varispeeded up by less than half a semitone during mixing) and is based on a G-D-Am7-C-D chord progression, with the G chord becoming an Em during the pre-chorus, though the key changes to A minor following the last chorus.
The song begins with a voice whistling briefly and saying "Oh yeah", followed by a drum beat that plays unaccompanied for a few measures.