The Japan star, a former team-mate of Mata at Manchester United, is the 18th footballer to join the pledge to donate one per cent of his salary to a charitable fund.
"Football has given me so many opportunities in life and now I want to play my role in supporting others through the game," Kagawa said.
"Common Goal is quickly growing around the world and I'm proud to help lead the movement forward in Japan.
"I've been fortunate enough to have football lead me all over the world ... If there's one constant I've witnessed throughout the journey, it has to be passion.
"Football inspires and excites people like nothing else on the planet, and what I love about Common Goal is that it channels this passion in a way that makes a real difference to disadvantaged communities around the world."
Mata said: "Shinji knows a thing or two about being first. He was the first player from Japan to play at Manchester United and then the first to win the Premier League.
"So I think it's fitting that he's now the first to join Common Goal as well. I know first-hand that Shinji is a special footballer and a brilliant person. It's a great pleasure for me to welcome him to the team."
Juventus defender Giorgio Chiellini and Bayern Munich's Mats Hummels are two of the highest-profile players to have joined Mata's cause, while Sydney FC captain Alex Brosque is also a supporter.
Swansea City's Alfie Mawson and Bournemouth's Charlie Daniels are the first Premier League players to have signed up to the initiative, which also boasts the support of a number of past and present stars of the women's game, including USA forward Alex Morgan and Arsenal Ladies midfielder Heather O'Reilly.