Sister Parish began her career in 1933 in Far Hills, New Jersey. The New York Times noted "Mrs Parish's six decades of decorating epitomized the rise of women in her own and other professions in 20th century America. The one-person business she started during the Depression evolved into the noted firm Parish Hadley Associates, whose clients included, among others, President and Mrs. John F Kennedy, and a veritable list of Who's Who in America".
As Architectural Digest noted in 2000, few firms had a greater impact on interior design than Parish Hadley and the partnership between Sister and Albert Hadley influenced American decor for more than three decades. Sister was widely considered to have originated the decorating idiom that became known as the American country style and her firm was known to be champion of American crafts and craftsmanship.