Armantrout was born in Vallejo, California. An only child, she was raised among military communities on naval bases, predominantly in San Diego. In her autobiography True (1998), she describes herself as having endured an insular childhood, a sensitive child of working class, Methodist fundamentalist parents. In 1965, whilst living in the Allied Gardens district with her parents, Armantrout attended San Diego State University, intending to major in anthropology. During her studies she transferred to English and American literature, later studying at the University of California, Berkeley. At Berkeley, she studied with poet Denise Levertov and befriended Ron Silliman, who would become involved with the Language poets of late 1980s San Francisco. Armantrout graduated from Berkeley in 1970 and married Chuck Korkegian in 1971, whom she had dated since her first year of university.

Armantrout has twice received a Fund For Poetry Grant and was a California Arts Council Fellowship recipient in 1989. In 2007 she was awarded a grant from the Foundation for Contemporary Arts Grants to Artists Award. She is currently one of ten poets working on a project entitled The Grand Piano: An Experiment In Collective Autobiography. Writing on the volume began in 1998 and the first volume (of a proposed ten) was published in November 2006, and thereafter in three-month intervals.

Wobble, to be published in November 2018, is a finalist for the 2018 National Book Award for Poetry.