Alyson was born in Washington, DC in 1974. Her parents divorced in 1976 when she was only 2, and by 1978 she was living in Atlanta and working in commercials for Oreos, McDonalds, and Six Flags Amusement Parks.
In 1985 she moved from Atlanta to Los Angeles and began to pursue her acting career in earnest. She was casted in many movies but none of them gained her fame, until she auditioned for "Buffy the Vampire Slayer." Although the part for Willow had already been casted, everyone was so impressed by Alyson's audition, that they gave her the part. She worked on the series for seven seasons.
Her work on the big screen includes such hits as "My Stepmother is an Alien" (1988) and the successful "American Pie" movie series (1999-2012). She is proud of the success that the "American Pie" movies have found, and she is now widely known for being the "Band Camp Girl."
She and "Buffy" co-star Alexis Denisof were married in October of 2003. In 2009 they welcomed the birth of their daughter Satyana Marie Denisof. She can currently be seen on the television show "How I Met Your Mother."