The organization said Tuesday that it is receiving the funding from Soros' Open Society Foundations.
The grant challenges Human Rights Watch to raise an additional $100 million in matching private contributions.
It will require Human Rights Watch to increase its annual budget from $48 million to $80 million within five years.
Soros said in the statement that human rights are "at the heart of open societies."
The international human rights group is based in New York and is supported by contributions from individuals and foundations.