A man charged with the targeted killing of a Minnesota lawmaker and her husband in what prosecutors described as an act of political violence has pleaded guilty, avoiding a potential death penalty under a plea deal.

Vance Boelter said he shot and killed Democrat Melissa Hortman and her husband, Mark, at their Minnesota home last June. Boelter also admitted to shooting state lawmaker John Hoffman and his wife Yvette, in their home. The couple survived the attack.

Boetler, 58, pleaded guilty to six counts, which include murder and stalking, and is expected to spend the rest of his life in prison.

The attacks on lawmakers come amid heightened concern about political violence in the US.

"The Attorney General has authorized and directed the government not to seek the death penalty against Defendant Vance Luther Boelter in accordance with the terms delineated in a proposed plea agreement," he wrote.

Prosecutors are seeking two life sentences, plus 40 years for Boetler.

The sentencing is expected next month.

The deal reflects an agreement on federal charges; the state of Minnesota still has to resolve its case against him, state officials said.

The state charges include premeditated murder, attempted murder, cruelty to an animal and impersonating an officer.

The attack came amid increasing concerns about attacks on lawmakers, and prominent political figures.

Months earlier, an arsonist set fire to the home of the Democratic Governor of Pennsylvania.

Three months after the Minnesota attacks, conservative commentator Charlie Kirk was shot during a speaking event at a university in Utah.

US President Donald Trump has also been the target of several assassination attempts, including most recently at a gala at a hotel in Washington DC in April. (BBC)