Johnson grew up in Lilburn, Georgia, where he attended Brookwood High School.[4] For a brief period he attended school in California where he played for his high school in Los Angeles County. He would graduate from there in 2005.
Sean Johnson was drafted in the fourth round (51st overall) of the 2010 MLS SuperDraft by Chicago Fire.[7] He was the last Generation Adidas player selected in that draft. 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. In his rookie season, he earned back to back "Save of the Week" honors. In 2013, he was named the Chicago Fire's Defender of the Year. He had an 11–9–7 record with the Fire, including with 6 clean sheets.
On December 11, 2016, Atlanta United acquired Johnson from the Chicago Fire for general allocation money. Later that day New York City FC acquired Johnson from Atlanta United in exchange for general allocation money and target allocation money.[8] He made 206 total appearances for NYCFC and won the 2021 MLS Cup with the club as their starting goalkeeper.
On January 27, 2023, Johnson signed a two-year contract with Toronto FC.[9]
International career
Johnson holds United States and Jamaican citizenships.[10] He had brief tryouts with the Jamaican under-17 team in 2005 and under-20 team in 2008.
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. He served as second choice keeper to Nick Rimando during a pre-tournament friendly against Guatemala and for the duration of the tournament. 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. During that game he made a key save in the 80th minute which led to the US's winning goal. The start officially cap-tied the dual-national Johnson to the United States.[10]
On November 9, 2022, Johnson was named to the United States's roster for the 2022 FIFA World Cup.[14] He did not play during the tournament, serving as a backup to Matt Turner.