Is it permissible to work as an accountant in the investment department of a governmental body headed by the Minister of Finance, knowing that the work of the department is mixed, not all of it being permissible (halal)?

Working in governmental institutions, such as the Investment Management, is permissible if the field of work is lawful. If an accountant's work is limited to legitimate transactions, paying salaries, and managing properties, then it is permissible for him to remain in it; otherwise, his work would be forbidden. This is in accordance with the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression."