Nebraska legislators overrode a veto from the state's governor, Republican Pete Ricketts, with the bare minimum number of votes needed to force through a bill in the state's unicameral legislature.
Ricketts vetoed the bill last week, arguing the state should at least have the option to pursue capital punishment to protect the public, even if used rarely.
"My words cannot express how appalled I am that we have lost a critical tool to protect law enforcement and Nebraska families," said Ricketts in a statement after the vote. "While the Legislature has lost touch with the citizens of Nebraska, I will continue to stand with Nebraskans and law enforcement on this important issue."
No Republican-controlled state has outlawed the death penalty in over 40 years.
"We are a nation that is turning away from the death penalty. This victory stands as a testament to what can happen in our sister states," Danielle Conrad, the executive director of the Nebraska chapter of the American Civil Liberties Union, said in a statement.
Still, in a CNN/ORC poll last month, only 27% of respondents said they felt the death penalty constituted "cruel and unusual" punishment.
Republicans have traditionally supported the death penalty, endorsing the option in the GOP's 2012 platform for those convicted of capital murder. But the Republicans' traditional tough-on-crime mantra has begun to soften, with power players like presidential candidate Rand Paul and GOP megadonors Charles and David Koch arguing that the party needs to change its tune on criminal justice issues.
Six states have abolished capital punishment since 2007 -- Nebraska is now the seventh.