Acker was born in Dallas, Texas, to Robert Acker, a lawyer, and Sandra Bruyere, a housewife of French ancestry. She is the oldest of four children and the cousin of Joel Jeffrey Acker. Acker studied ballet, modern dance, and jazz dance for 13 years. She underwent knee surgery while in high school, ending her ballet career, and she began to study acting in her sophomore year. She enrolled at Southern Methodist University in 1995 to take advantage of that school's renowned theatrical program.
In her junior year of college, Acker enjoyed a short stint of modeling work for the J. Crew clothing catalog. In 1999, she was nominated for a Leon Rabin award for "Outstanding Performance by an Actress in A Lead Role" for her performance in the play Therese Raquin. She received a Bachelor of Fine Arts degree in the same year.
Acker appeared as Winifred "Fred" Burkle on the second through fourth seasons of Angel and as Burkle/Illyria for the fifth and final season. She won the 2003 Saturn Award for Best Supporting Actress on Television for her portrayal. On April 25, 2003, Acker and actor James Carpinello were married in California. On January 22, 2005 she gave birth to a son, Jackson James Carpinello, and on September 1, 2006, a daughter, Ava Grace. In 2005, she joined the cast of Alias for its final season, playing the villainous Kelly Peyton. Acker graduated from guest star to fully credited cast member as the show entered the final episodes in April and May 2006.
Acker guest starred on fellow Buffyverse actress Alyson Hannigan's new show How I Met Your Mother, in which she was reunited with Angel co-star Alexis Denisof, who has a recurring role on the show.
