Can a professor of iim start an ngo for social causes

Full time employee in itself would imply no other engagement.

One may believe that this engagement is limited to gainful employment.

However the language in standing orders of the organization, appointment letter, service rules, HR policy, conduct rules should be carefully studied.

Some establishments may encourage/allow CSR but may put a cap on time and involvement.

Organizations are known to have rules even on leaving activities HQ with/without permission.

To be on safer side it shall be appropriate to discuss with good offices of appointing authority, HR Head, Director, Admin and appraise them on purpose, intent and limit of  involvement, position/designation, honorarium etc and obtain NOC in writing.

A lawyer can help to register NPO/NGO as :

Trust ; as Trust NGO (private trust, public charitable trust.) for doing charitable work, under Indian Trust Act 1882 or public Charitable Trust Act of the State. Private Trust may not get tax benefits.

Society : under Societies Registration Act, 1860.

Valuable advice of learned experts/members is sought.

Dear,

A govt. employee can not run any NGO or be a member of the NGO/Trust/Society as a governing body or executive member.

regards

You can do so with prior permission of the department.