Born in Manitoba, Canada, in 1917, Sandgren grew up in Portland and Chicago. He received his art education at the Chicago Institute of Design, the University of Oregon, the University of Michoacan, Mexico, and earned both his B.A. and M.F.A. at Oregon State College (now Oregon State University). After graduation in 1947, he joined the faculty there, and served as a professor until his retirement in 1987.
Nelson was greatly influenced by his teachers at the University of Oregon - David McCosh, Andrew Vincent and Jack Wilkinson, and although he did not study with her, Sandgren shared art philosophies with Maude Kerns in the later years of her life.
In 1947 and 1948, Nelson studied with a second major influence in his work, Mexican muralist Alfredo Zalce, in Morelia, Michoacan.
He became interested in creating larger scale paintings in collaboration with fellow artist friends. His public murals include those found at Mahlon Sweet Airport and the Lane County Court house in Eugene, Oregon, and also the Kerr Memorial Library at OSU, in Corvallis. He received numerous awards,
grants and commissions during the course of his career, and exhibited in England, California, and
Colorado, as well as Seattle and Portland.
A prolific artist, Sandgren spent four to five hours a day working in his studio, using oil, watercolor, and various print-making techniques. His unique brush work captures the essence of the environment in simplified, dynamic strokes. A sense of fearlessness and delight, as well as reverence for the beauty of the natural world and the people in it, permeates his work. Though Nelson traveled widely, his interest in the Oregon Coast never waned. He founded of a group of plein air painters, which, for a number of years, congregated at the beach in Bandon. His son, Erik Sandgren, carries on this tradition, with yearly coastal paint-outs, which continue to be a highlight in the experience of many local artists.