Pappas became politically involved in 2018 when she became an elected precinct committeewoman with the local Democratic organization in Addison Township. In the summer of 2018, Pappas was nominated by the local Democratic organizations in the district to run against the then-unopposed Republican incumbent Christine Winger. Pappas narrowly defeated Republican incumbent Christine Winger with 50.8% of the vote to represent the Republican-leaning district.
Tenure
Pappas was sworn into office on January 9, 2019. During the 101st General Assembly, Pappas served on the following committees: Adoption & Child Welfare; Cities & Villages; Cybersecurity, Data Analytics, & IT; General Service Appropriations-General Service; and Prescription Drug Affordability.
Pappas proposed the creation of an income tax credit in an amount equal to the amount paid by the taxpayer for purchasing acoustical materials, other materials, labor, and professional services to soundproof a residential home located near airports against aircraft noise. This credit, if passed, would have allowed constituents living near O'Hare International Airport's new flightpaths to soundproof their homes.
Healthcare
Along with Deb Conroy, Pappas introduced legislation to provide coverage for the treatment of serious mental illnesses and serious emotional disturbances. Diane Pappas is pro-choice on abortion and voted for the Reproductive Healthcare Act. Dan Proft's conservative political publications and Republican legislators Mark Batinick and Darren Bailey criticized Pappas for an alleged remark that invoked castration when speaking about female autonomy at a town hall.
Tax reforms
Pappas proposed House Bill 338 which would create an assessment freeze homestead exemption for persons receiving federal Supplemental Security Income; a means tested program that is part of the Social Security Act. Pappas voted to place a referendum on the 2020 general election ballot that would allow the state of Illinois to repeal its current flat tax structure in favor of a progressive tax structure if passed by 60% of voters. Pappas supported Senate Bill 1217, which lowered the amount of money that municipalities are required to devote to tourism from the hotel/motel tax from 100% to 75%. The change had been long sought by local leaders in smaller towns to fund economic development efforts and infrastructure improvements.
