Who discovered the Indus Valley civilization?

Sir John Hubert Marshall led an archaeological expedition in 1921-1922. It was during this expedition when Harappa was discovered. Marshall and Sir Mortimer Wheeler then excavated Mohenjo-Daro in 1931. Thus we can safely say that Sir John Hubert Marshall is credited for discovering the Indus Valley Civilization

For further reading check the following articles:

• Prehistoric Age in India
• Prehistoric Rock Paintings