Johnson worked for the office of the South Dakota Secretary of State for eight years. She announced her candidacy for the 2022 election for secretary of state in February 2022. She challenged the incumbent, Steve Barnett, for the Republican nomination at the Republican convention on June 25, and won the nomination. During the campaign, Johnson refused to acknowledge that Joe Biden was the legitimate winner of the 2020 United States presidential election. She defeated Democrat Tom Cool in the November 8 general election. Barnett resigned from office in December, and GovernorKristi Noem appointed Johnson to the office effective December 5, and her own term began on January 2.
In January 2025, Johnson announced that she would run for a second term in the 2026 election. She lost the nomination to Heather Baxter at the state party's convention on June 27, 2026. On September 19, Johnson crossed party lines to endorse the Democratic candidate Terrence Davis.
1 ▌New Progressive (1 territory) Italics indicate no secretary of state in this state, closest equivalent listed An asterisk (*) indicates that the officeholder is serving in an acting capacity.