Preeti Rathi, who was 23 when she was attacked, had just arrived from Delhi to join the Indian navy as a nurse.
Her neighbour, Ankur Panwar, had said he attacked her because she had rejected his proposal to marry him.
The verdict is significant as most attackers receive minor sentences.
Panwar, 25, was convicted of murder and other offences on Tuesday. He is likely to appeal the verdict in a higher court.
On Thursday, the court said that the crime fell within the "rarest of rare" category which justified the death penalty.