She began at TIME as a writer in 1979 and served as its medical writer from 1982 through 1987. In 1987, she became the third woman in the magazine's history to be named a senior editor. Ms. Wallis served as managing editor of TFK from 1995 through May 2003. She oversaw the creation of three separate editions, each focused on a different age group, as well as the launch of a successful spin-off magazine called Go Places with TFK.

Ms. Wallis has written more than 20 cover stories for TIME. Among them: "How to Make Your Kid a Better Student" (1998), which won First Prize in the Education Writers Association Awards; "Faith and Healing" (1996), "Stress" (1983), "Cholesterol" (1984), "AIDS" (1985), "Child Care" (1987), "Women Face the 90's" (1989), "Breast- Cancer" (1991), "Pills for the Mind" (1992), "Attention Deficit Disorder" (1994) and "Estrogen" (1995). Her writing has won citations from the National Mental Health Association, the Newspaper Guild of New York, the Susan G. Komen Breast Cancer Foundation and the Newswomen's Club of New York, among other organizations. In addition, her cover stories on cholesterol and attention deficit disorder were finalists for the National Magazine Awards.

As a senior editor, she was responsible for dozens of TIME covers, including those on "Who was Jesus?" (1988), "Adoption" (1989), "Vitamins" (1992), "The Ice Man" (1992), "Dinosaurs" (1993), "The Info Highway" (1993), "Sex in America" (1993). In 1990, she presided over TIME's special issue "Women: The Road Ahead", which won a special citation from the National Women's Political Caucus.

Ms. Wallis graduated Yale University in 1976, summa cum laude and Phi Beta Kappa, with a degree in philosophy.