Green’s Dictionary of Slang

1. (Aus.) a traveller who rides from station to station.

1920

Bulletin (Sydney) 19 Feb. 26/2: They are up to date in their slang in the Northern Territory. The swagman on horseback who wanders from station to station is called a ‘looper’ because he goes round and round like an airman looping the loop.

2. a caddie.

1981

J. Ellroy Brown’s Requiem 23: Loopers got dirty mouths.