Smith is best known for her roles in the daytime soap operas. She made her soap debut in 1982, as Kit McCormick on The Doctors and one year later, taking over the role of Margo Hughes on As the World Turns, a role she played from 1983 to 1990.

Smith was born as Hillary Bailey in Boston, Massachusetts. She attended Dana Hall School, Pine Manor College and Sarah Lawrence College. At Sarah Lawrence as a senior, she performed in off Broadway and Broadway productions, including The Heidi Chronicles. She married Philip Webster Smith, III in 1983. She met her husband at age 14 and married him a few years later after the two reconnected at a friend’s wedding. They have two children, a daughter, Courtney and a son, Philip. (As an infant, Smith’s son played her on-screen son briefly on As the World Turns.)

After taking maternity leave from acting after the birth in 1988 of her son, Smith returned to daytime television, originating the role of Llanview District Attorney Nora Hanen Buchanan on ABC soap opera One Life to Live. Character she has played from 1992 until the series’ cancelation in 2012. She later returned to show in the 2013 The Online Network short-lived continue. Smith won the Daytime Emmy Award for Outstanding Lead Actress in a Drama Series in 1994, for her performance in One Life to Live. From 1994 to 1995, Smith also has starred as lead in the NBC sitcom Something Wilder.

Smith appeared and produced web soap-type series Venice: The Series. As producer, in 2014 she has won Daytime Emmy. In 2014, Smith was the supervising producer for the soap opera web series Beacon Hill, and was nominated for a 2015 Daytime Emmy for Outstanding New Approaches Drama Series. In late January 2017, it was reported by Soap Opera Digest and Deadline Hollywood that Smith will reprise her OLTL character on General Hospital.