The daughter of a well-to-do family from Brooklyn, Laura Leggett married Albert Barnes in 1901. Though the origin of Laura’s interest in horticulture is unknown, there is evidence that she managed the gardens at the couple's first home in Merion, Lauraston. When they moved to the Barnes Foundation's new home in Merion, Laura devoted herself to the development of its Arboretum.
Laura Barnes became director of the Arboretum in 1928, and founded the Arboretum School in 1940, where she was an instructor. She was responsible for the acquisition of plants for the gardens, and she corresponded and exchanged specimens with many other notable collections, including the Arnold Arboretum and the Brooklyn Botanic Garden. Mrs. Barnes also maintained a personal library of horticulture books, which are now held in the Foundation's Rare Books Collection. In recognition of her horticultural efforts, she was awarded the Schaffer Memorial Medal from the Pennsylvania Horticultural Society in 1948, became an honorary member of the American Society for Landscape Architects in 1955, and received an honorary doctorate in horticultural science from St. Joseph's University.
Following her husband's sudden death in 1951, Laura Barnes succeeded him as president of the Foundation. Though her primary legacy lies in her contributions to the living collections of the Barnes Foundation, she also purchased art. Her private art collection was donated to the Brooklyn Museum after her death in 1966.