Can I work as a freelance academic writer for websites like www.ukessays.com or www.bestessays.com? What's the sharia law about this kind of part-time writing profession?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

If the work of the two mentioned sites is restricted to preparing essays for the students and solving the exercises that are given to them by the schools and universities so that they would do it by themselves, then preparing such essays for them is considered as cheating the body [authority] which entrusted them to do it and this will corrupt the education. Hence, it is not lawful to work in such kind of work as Allaah Says (what means): {... but do not help one another in sin and transgression.} [Quran 5:2]

Therefore, it is neither permissible to work for those two sites nor to cooperate with them in such falsehood and cheating which are both forbidden.

However, if they have other lawful tasks, then it is permissible for you cooperate with them in achieving them either as a part-time work or else.

Allaah Knows best.