Ankit Saxena, 23, a photographer by profession, had been in a relationship with Shehzadi, 20, for the last three years.
"The woman's family was against their relationship as they belonged to different communities and had told him to end it," Deputy Commissioner of Police, Vijay Kumar, said.
The attack took place around 9 p.m. and was reported to the police by a hospital staff, the police said.
Ankit's father Yeshpal Saxena said it was a case of honour killing as the accused were carrying knives and had planned to kill his son.
"We did not know about the relationship of Ankit and Shehzadi. We asked Ankit once but he denied it.
"Shehzadi's family came here on Thursday and told Ankit to come out of the house. When he did, they started beating him up on the street," Sexena said.
"When his mother came to his rescue, she too was beaten up mercilessly. Then Shehzadi's brother slit Ankit's throat as the other family members held him. They fled before police reached the spot," he added.
In a bid to avoid any untoward incident since the deceased and the accused belonged to different communities, police have tightened the patrolling in the area, the officer said.