In January 2011, longtime state representative Mike Obuchowski stepped down from the legislature to become Vermont’s Commissioner of Buildings and General Services.
On January 21, 2011, newly elected governor Peter Shumlin announced that he had selected Trieber to fill Obuchowski's seat representing the Windham-4 district.
[3] Trieber ran for election to the Windham-3 seat in 2012, after redistricting changed the composition of the state's districts.
[4] Trieber faced Christopher Moore and Rep. Carolyn Partridge in the primary election held on August 29, 2012 and finished second, giving him a place on the November ballot.
[6] He is one of six openly gay members of the Vermont Legislature, alongside representatives Bill Lippert (D–Hinesburg), Herb Russell (D–Rutland) and Joanna E. Cole (D–Burlington), as well as senators Brian Campion (D–Bennington) and Becca Balint (D–Windham).