The 35-year-old murderer killed his family members in early hours of Sunday at one of their homes in Thane, 20 miles from Mumbai, for a family function, according to police statement.
Neighbours were alerted to the attack by the screaming of the man’s sister, who survived the attack.
Reports suggest Hasnin Warekar laced his family’s food with sedatives before slitting their throats.
“The attacker, Warekar, hung himself after slitting the throats of all other family members,” police spokesman Gajanan Laxman Kabdule told the AFP news agency.
“We still haven’t been able to speak with the attacker’s 21-year-old sister, the lone survivor of the attack, who is in deep trauma at a city hospital,” Mr Kabdule said.
However, the Indian Express newspaper said the assailant stabbed his victims after they went to bed.
“Prima facie evidence suggests that the accused bolted all the doors of the house and murdered his family while they were asleep with a knife that we found near his body,” Ashutosh Dumbre, joint commissioner of Thane police, was quoted saying.