The daughter of Molly Ann, a judge, and Elliot Beitner. She has three older sisters, Katherin, Elizabeth, and Marie. Blair attended Hillel Day School, a Jewish day school in Farmington Hills, Michigan and Cranbrook Kingswood school in Bloomfield Hills, Michigan. She attended Kalamazoo College in Michigan, then later transferred to the University of Michigan, where she earned her bachelor's degree in 1994.
After training at the Stella Adler Conservatory of Acting, Blair began acting in the mid-90s. Blair began her career with small roles and guest roles in various television series. Blair went on to star as Zoe Bean in two seasons of TV series Zoe, Duncan, Jack and Jane, She rejoined actress Reese Witherspoon in the comedy film Legally Blonde.
Her stage work includes the role of Kayleen in Rajiv Joseph's Gruesome Playground Injuries, which had its world premiere at Houston's Alley Theatre in October 2009.