Gonzalez was signed to a minor-league deal in early May. After making one appearance with Triple-A Syracuse, the Nationals felt the left-hander was ready to contribute in the big leagues and selected his contract from Syracuse on Sunday.
The 34-year-old Gonzalez has 56 career saves. He pitched last season for Baltimore and Texas.
Washington general manager Mike Rizzo said of Gonzalez: "He's a very accomplished veteran. We thought it was a good fit for us at the time with some of the injuries we have in the bullpen."
The Nationals optioned reliever Ryan Perry to Syracuse and moved Storen (elbow) to the 60-day disabled list.