Johnson was a member of the Mississippi State Senate representing District 19 from 1995 to 2003 as a Republican.
Johnson announced on February 4, 2015, that he was switching to the Democratic Party to run for lieutenant governor.
[3] However, the primary reason Johnson attributes his decision to switch parties is Republican leadership's refusal to expand Medicaid in Mississippi.
He served with diction on the Finance, Insurance, Juvenile Justice, Municipalities and Veterans and Military Affairs Committees.
[6] On February 4, 2015, Johnson announced his candidacy for Lieutenant Governor against Republican incumbent Tate Reeves.
[3] In a Senate Resolution commending his "outstanding legislative record and dedicated service," Johnson is described as a champion of law enforcement, school choice and issues enhancing municipal government.