Officers were called to the privately run prison at around 4am where the man, identified in local media as Willem Van Spronsen of Vashon Island, had set a vehicle alight with the explosives.
He is also believed to have attempted to ignite a large propane tank outside the building.
His target, the Tacoma Northwest Detention Centre, has long served as a holding facility for migrants as they are about to be deported.
More recently it has also housed parents separated from their children at the border under Donald Trump’s “zero tolerance” policy towards undocumented immigrants.
The incident took place roughly six hours after a peaceful rally against deportations outside the centre.
Officers confirmed Van Spronsen was shot dead at the scene, with all four attending officers discharging their weapons.
He was described locally as a committed anarchist and antifascist. One friend of twenty years, Deb Bartley, told The Seattle Times she and others had received letters from him which read “just saying goodbye” along with what she described as a manifesto.
She added: “I think this was a suicide. But then he was able to kind of do it in a way that spoke to his political beliefs... I know he went down there knowing he was going to die.”
Van Spronsen is believed to have had previous run-ins with law enforcement at the detention centre.
In 2018 he was reportedly among ten people to be taken in by police after occupying the perimeter of the site – with the then 68-year-old arrested on suspicion of third-degree assault for jumping on the back of an officer as he attempted to apprehend another activist.