What is the religious ruling on a young man's refusal to work in law or the judiciary within a man-made legal system that contravenes the provisions of Islamic Sharia, and is administrative work in the Parliament that enacts these laws considered assistance in sin?

It is impermissible to work in a profession that necessitates ruling by laws contradicting Allah's Sharia (definition), or assisting in such. If one can limit their work in the legal profession, judiciary, or as a parliamentary consultant to cases that do not require ruling by other than what Allah has revealed – such as administrative cases, contract authentication, cases that conform to Sharia, or those that repel injustice from the oppressed – then there is no harm in that. However, if it is impossible to avoid cases that necessitate contradicting Allah's ruling, then working in these professions is forbidden, based on Allah's sayings: "Do they seek other than the religion of Allah?" and "Is it the judgment of [the time of] ignorance they desire?" and "Have you not seen those who claim to have believed in what was revealed to you and what was revealed before you? They wish to refer for judgment to Taghut [false deities/tyrants], while they were commanded to reject it." In such a situation, refraining from working in these professions is obligatory, and whoever gives up something for the sake of Allah, Allah will compensate him with something better.