Patricia Arquette has won the Best Supporting Actress Oscar for “Boyhood” for her incisive portrayal of a vulnerable single mother over a 12-year period.

Arquette has been the prohibitive favorite in the field since the awards season started, winning trophies at BAFTA, SAG, the Critics Choice, the Golden Globes and the Spirits.

She won over Laura Dern for “Wild,” Keira Knightley for “The Imitation Game,” Emma Stone for “Birdman” and Meryl Streep for “Into the Woods.” It was Streep’s 19th nomination and Arquette’s first.

Arquette, 46, was often cited by critics as one of the key factors in Richard Linklater’s groundbreaking film, shot in a dozen different segments between 2002 and 2013. Her portrayal of Olivia Evans managed to encapsulate the hopes and disappointments of her generation, portrayed with a transcendent honesty without frills.

Prior to “Boyhood,” Arquette had been best known for portraying a psychic in the supernatural drama series “Medium” for seven seasons, winning an Emmy in 2005. She also received strong critical support for starring in the last two seasons of “Boardwalk Empire.” and was the series lead in “Medium” from 2005 to 2011. Other notable roles for the actress include “Stigmata” and “True Romance.”

Arquette comes from a family of actors, including brother David Arquette, Alexis Arquette, Richmond Arquette, and Rosanna Arquette. She’s the first in the family to have been nominated for an Oscar.

Arquette read her acceptance speech from a sheet of paper, concluding a lengthy thank-you list with a well-received call for wage equality and equal rights for women in the United States.