Catherine Jane Stubbs, a German national who voluntarily returned to the US to face the charges, could be punished by life imprisonment at a December sentencing hearing.
Stubbs and other members of the late Bhagwan’s cult devised an unfulfilled plan to kill federal prosecutor Charles Turner, according to the US Attorney’s Office.
The cult members targeted Turner because he was investing whether Bhagwan followers at the 25,900-hectare commune in Oregon were commiting crimes that included illegal wiretaps and immigration fraud by sham marriages.
The fake marriages enabled Bhagwan’s foreign disciples, known as “sannyasins,” to remain in the United States, prosecutors said.
Bhagwan’s “second in command” Sheela Silverman enlisted her “closest subordinates” to kill Mr Turner, according to a written release.
Stubbs volunteered to be the assassin, bought guns, and spied on what cult members thought was the parking garage Mr Turner used at work, prosecutors said.
Stubbs, who also used the names Ma Shanti Bhadra and Catherine Jane Stork, took refuge in Germany.
She was indicted by a federal grand jury in 1990 and Germany refused to go along with efforts by US officials a year later to extradite Stubbs, according to prosecutors.
Stubbs returned to the United States of her own volition in September of 2005, asking for a deal, prosecutors said.
US District Court Judge Malcolm Marsh accepted her pleas to conspiracy and weapons charges then gave her permission to make a trip to Australia to visit a son who is suffering from incurable brain cancer, according to prosecutors.
Stubbs is to be sentenced in December.
Stubbs is the seventh and final indicted cult member convicted in connection with the alleged murder plot, according to prosecutors.
Sheela, a naturalised Swiss national immune to extradition, was convicted in 1999 by a Swiss court of “criminal acts preparatory to the commission of murder,” the Swiss equivalent to a US murder conspiracy charge, prosecutors said.