Grantier worked across a broad range of media — painting, weaving, ceramics, watercolor, block print, chalk, and wax sculpture — but it was clay that defined his public reputation. In 1935 he joined the staff of the Dickinson Clay Products Company, contributing designs to the Dickota and Badlands Pottery lines, which drew on native western North Dakota clay and regional imagery. His "Sundog" design — evoking the ice-crystal halos visible on cold plains horizons — was among his most distinctive contributions. Exceptional pieces from this period survive in the UND Pottery Collection.
From 1939 to 1942 Grantier served as Director of the WPA Ceramics Projects for North Dakota, building a Mandan-based operation that employed eighteen workers producing functional ware for hospitals and schools statewide. A number of the craftspeople he trained went on to work in pottery independently after the program's wartime closure. His expertise in the field was further recognized through a contributor credit in the Kovels' Collector's Guide to American Art Pottery.
In the postwar decades Grantier taught in rural communities across the state — among them Mott, Crown Butte, Hay Creek, and Menoken — while continuing to work across multiple media. In 1953 he received the Citation Award, earning a place on the Honor Roll of the American Artists Professional League, and was included that year in Jessamine Stancliff Barr's North Dakota Artists, the definitive survey of the state's artistic community. He served as founding president of the Mandan Art Association (1958–59), chaired its inaugural art show, and became Mandan High School's first art teacher when the subject entered the curriculum. Beyond his own classroom, he played a central role in developing the first statewide course of study for high school art instruction in North Dakota — a contribution that shaped arts education across the state for a generation.
A dedicated collector of antiques, Grantier assembled an extensive household of early American pieces and was known for an exceptional collection of fish-pattern dishware and glassware.
Grantier died on February 6, 1979, and is buried alongside his wife Minnie in Union Cemetery, Mandan. His painted works are rare in collections; the Leno Family Collection in Fargo, ND, holds one known watercolor.