It is definitely a member of Fabaceae (the legume family), which doesn't help much as there are 12,000 species in it (including all the suggestions so far. It doesn't look like Medicago, it's definitely not Robinia suckers and I'm not convinced its Swainsonia (not enough leaflets, flower panicle is too dense).
If it is growing as a vigorous weed it may well be non-native (perhaps South African?) and thus not in Australian 'wild flower' type books. FWIW I am a botanist, though a physiologist so my taxonomy is limited and coming from the UK originally, it is even more limited when it comes to Australian plants. Doesn't look European though.
Sorry, not much help really!
