1. Complaint is defined under section 2(d) of CrPC.
FIR is given under Section 154 of CrPC.
2. Complaint is an allegation which is made orally or in writing to a magistrate.
FIR is given to an officer in charge of a police station.
3. A complaint may relate to a cognizable offence or non-cognizable offence.
FIR is related to a cognizable offence.