Alyson Lee Hannigan came into the world on March 24, 1974 to a mother who was a real estate agent and a truck driver father. After her parents' divorce when she was just a year old, she and her mother moved from Washington, D.C. to Atlanta where she was subsequently raised.

She began acting as a child, starring in numerous TV commercials. Her premier movie role was in the 1988 sci-fi comedy "My Mother Is an Alien" where she got the chance to work with fellow actor Seth Green who would later also become her co-star in the hit TV show "Buffy the Vampire Slayer". In 1989 she got the lead role in a in a TV series called "Free Spirit". Unfortunately the series only lasted one season and Hannigan went back to doing commercials for most of the early 90s. In 1997, she got the role of Willow, one of the main characters in "Buffy the Vampire Slayer".

As the show's popularity grew so did Alyson's and she was able to get parts in teenage films such as "American Pie" (1999), "Boys and Girls" (2000), "American Pie 2" (2001) and "American Wedding" (2003). Buffy stopped airing in 2003 after a seven year run, and by the time the show ended Alyson was making a quarter of a million dollars per episode. Since 2005, she has had one of the lead roles in another hit TV series called "How I Met Your Mother".

Privately Hannigan has been involved with Ginger Fish, one of the members of Marilyn Manson as well as fellow actor Alexis Denishof whom she married in 2003. The two are still together and have a daughter by the name of Satyana Marie Denisof who was born on March 24, 2009, the same day as her mom.