During his college years Johnson also played one season with Atlanta Blackhawks in the USL Premier Development League.

He made his MLS debut on August 1, 2010, during a 3–2 victory over Los Angeles Galaxy after earning the starting spot over Andrew Dykstra.

On December 11, 2016, Atlanta United acquired Johnson from the Chicago Fire for general allocation money.

After an injury to Bill Hamid, Johnson entered the game on the 39th minute of the last group match against El Salvador.

[12] Johnson earned his first senior cap for the United States national team entering as a halftime substitute in a friendly match against Chile on January 22, 2011.

[13] Johnson was named one of three goalkeepers assigned to the United States's 2013 CONCACAF Gold Cup roster by coach Jurgen Klinsmann.

Johnson earned his first senior national team start on July 17, 2013, in the final match of the group stage, recording a clean sheet in a 1–0 victory against rival Costa Rica.