He roamed the woods with the family dog, became an avid birder, and studied natural history, especially botany, under the mentorship of Mabel Hinde James.
During their marriage of over 47 years, she accompanied him on his bryological collecting trips and collaborated on several scientific projects.
[5] For several years he worked on a research project, the Generic Flora of the Southeastern United States, led by Carroll Emory Wood Jr. For five and one-half years ending on June 30, 1980, Miller was the supervisor of the Gray and Arnold Arboretum Herbaria and chair of the Herbarium Committee, and then continued on the staff as botanist at the Gray Herbarium and the Arnold Arboretum.
[6] In 1983 he joined the staff of the New York State Museum and eventually retired there as emeritus curator of bryology and Quaternary paleobotany[2] He was on the editorial boards of ten journals.
His field work in these areas led him to explorations throughout the northern latitudes from New York and New England to Michigan, Colorado, the west coast, the southeast, Alaska, Russia, Scandinavia, Scotland, Iceland, Greenland, Canada and Japan.