In 1955 McGarrell had his first solo exhibition at the Frank Perls Gallery in Beverly Hills and received a Fulbright grant to the State Academy of Fine Arts Stuttgart, Germany.
After returning from Germany in 1956, McGarrell began a long distinguished academic career at Reed College in Portland, Oregon.
During the past half century McGarrell had more than a hundred solo exhibitions at galleries and museums in America, England, France, and Italy.
His work has been included in: five Whitney Annuals and Biennials; the Carnegie International exhibition twice (1958 and 1983); New Images of Man at the Museum of Modern Art, New York City (1960); the Dunn International at the Tate Gallery, London (1963 and 1964); Documenta III (1964)in Kassel, Germany; and USA Art Vivant at the Musée des Augustins, Toulouse, France.
In 2003 several of his paintings were included in La creazione ansiosa: da Picasso a Bacon, a survey exhibition of later 20th-century art at the Palazzo Forti, Verona, Italy.