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.
Ms Rathi, who suffered severe injuries to her lungs and eyes in the attack on 2 May 2013, died a month later.
A month after her death, India's Supreme Court ordered federal and state governments to regulate the sale of acid.
The court ruled that acid could only be sold to people who showed a valid identity card. However, critics say that it is still widely and easily available.
According to government figures, there are hundreds of such attacks a year; but campaigners say the real figures are much higher.