Mata called for high profile players to sign up to the cause in the same week Neymar signed for Paris St-Germain for a world record £200m (222m euro).
Bayern Munich's Hummels said: "This is a chance for football to improve our world, and I wanted to be part of it."
The defender, 28, joined the German champions in May 2016, for around £30m.
"I feel we could be doing more to connect the increasing revenues in football to some kind of deeper purpose," he added.
"Through the 1% pledge, we're building a bridge between football and its social impact around the world."
Mata is raising money for Common Goal, run by the organisation streetfootballworld, after being shocked by the poverty he saw on a visit to Mumbai, India.
The 29-year-old Spaniard is aiming to create a 'Common Goal starting XI', made up of 11 players who each donate 1% of their wage to the charity and he said Hummels was the "perfect team-mate".
"He really gets what we're trying to achieve. The fact that a World Cup holder - at the peak of his career with one of the biggest clubs on the planet - has chosen to make the pledge shows the power and magic of what we're doing."
Germany's World Cup winner Mats Hummels is the first player to join Manchester United's Juan Mata in pledging to donate 1% of his wages to charity.