It was not until the passing of the Crimes (Sexual Assault) Amendment Act 1980(NSW) did it was possible that a husband be convicted of rape.

I don't find it completely OK. 
«It was not until the passing of the Crimes (Sexual Assault) Amendment Act 1980(NSW) that it became possible to convict a husband of rape»
The "... did it was" part in the original sentence doesn't make any sense

Thanks for your reply Ant_22. I wasn't sure about the 'did it was' part as well. Perhaps somebody could shed some light on this.

Thanks again

PBF

It was not until the passing of the Crimes (Sexual Assault) Amendment Act 1980(NSW) did it was possible that a husband be convicted of rape.

Uhm, how about this:
It was not until the passing of the Crimes (Sexual Assault) Amendment Act 1980(NSW) that it was possible for a husband to be convicted of rape.

@ Native speakers: please come in and let us know your opinions a

I prefer the "that it became possible" phrasing of the two given, but what about this:

Only after the Crimes [etc]... (NSW) was passed could a husband be convicted of raping his wife.

I think you need "his wife" in there, either way.

PrinnySquad:

Hope you won't mind if I give you some feedback on your version.
1. «...that it was possible...» — I do think it is better to use "became possible", because whereas "was" reflects a state, "became" referes to a change of state (i.e. an action), which is certainly better (IMHO).
2. «...possible for a husband to be convicted of rape...» — it is technically correct but

There's no need for the past perfect. Only if you wanted to use a specific instance, for example: "Because the law had just been passed, police were able to bring charges...." would the past perfect be preferable.

(In fact, it could possibly even imply that something had happened to "unpass" it later - that it was later repealed, for example.)