A committee of Democrats from Senate District 19 selected Zenzinger for the position on Tuesday night.
Zenzinger replaces Senator Evie Hudak who resigned last month
to avoid a recall election and ensure the seat stayed in Democratic hands. Zenzinger beat one other nominee for the appointment: former state representative Sara Gagliardi.
In order to hold the seat, Zenzinger will have to survive an election next November where voters in the highly-competitive district are almost evenly divided between Democrats, Republicans and unaffiliated.
Zenzinger said in a statement after the selection that she plans to focus on economic development, job creation, education, transportation and healthcare.
Colorado's state Democratic party chair Rick Palacio called Zenzinger a "pragmatic leader."
"The skills that you build on a city council are very translatable to the skill set needed to work with people of divergent viewpoints in the legislature," Palacio said. "And I’m sure she’s going to be very good at that."
Conservatives wasted little time in attacking Zenzinger.
"Sen. Hudak's consituents were hungry for change and liberal activists served up more of the same," Kelly Maher, spokesperson for the group Compass Colorado, said in a statement.
Maher also pointed out that Zenzinger had served as Hudak's campaign manager.
Zenzinger will be sworn into the state Senate on Friday.