Schreiner began his career as a recruitment representative for
Montana State University. After earning his Master's Degree, Schreiner worked as a middle school science teacher in the
Great Falls Public School System and at
Butte Central Catholic High School. Schreiner was elected to the
Montana House of Representatives in 2013, succeeding
Trudi Schmidt. As Minority Leader, Schreiner succeeded in extending Medicaid expansion, which brought government-funded health care to nearly 100,000 low-income families; funding education; and passing a comprehensive infrastructure package. In the
2020 Montana gubernatorial election, Schreiner was a candidate for governor until withdrawing from the Democratic primary on February 3, 2020. On February 28, 2020, candidate
Mike Cooney selected Schreiner to serve as his running mate. Cooney became the Democratic nominee in the June 2, 2020 primary election. Schreiner and Cooney faced incumbent Congressman
Greg Gianforte and Kristen Juras in the November, 2020 general election, where they were unsuccessful in their bid for governor and lieutenant governor. ==Personal life ==