Gjertson attended the University of Minnesota, where he majored in art, but was discouraged by the useless university art classes and left after three years to attend art school. There he encountered the same fascination with negative, theory-centric art and learned nothing of practical value. In 1971 he met Richard Lack (1928–2009) and studied art seriously until 1975 at Atelier Lack, a studio-school based upon the teaching of the 19th century French ateliers and the Boston impressionists.
Since 1975 Gjertson has created a diverse body of work that includes still lifes, landscapes, genre, portraits, and biblical/symbolic subjects. His artistic interests include both the impressionist tradition, with its emphasis on painting the world around him, and the academic tradition, with its emphasis on literary subjects and idealization. In the early 1970s, a fellow student introduced Gjertson to the work of Henri Fantin-Latour. He was deeply impressed by Fantin’s still lifes, particularly those from 1866. They, and a marvelous still life by the little-known Frenchman, Johanny Maisiat, have established the direction of his elegant still lifes, for which he has gained a considerable reputation.
At the beginning of his career Gjertson and his wife became Christians. The early interest that he had in paintings inspired by literature has led him to accept occasional commissions for works with biblical themes, such as Peace, Be Still and The Hem of His Garment. As time and finances have permitted, he has painted works with themes from both the Old and New Testaments and symbolic works, such as Rachel Weeping for Her Children, that deal with contemporary issues.
Gjertson dislikes labels, preferring to simply call himself a traditional realist. However, he is known as a “Classical Realist,” a designation that has passed into general usage in the art world. His teacher, Richard Lack, coined the term in 1982 to differentiate the realism of the heirs of the Boston tradition from that of other representational artists. It was first used in the title of the traveling exhibition, Classical Realism: the Other Twentieth Century.
Gjertson has organized and exhibited in over fifty exhibitions featuring the work of contemporary realists and impressionists. He has also been intimately involved with organizations that promote the work of artists within the classical realist tradition, most recently The American Society of Classical Realism. In 1989 he was a founding member of its Guild of Artists and acted as an editorial advisor to their publications, the Classical Realism Quarterly and the Classical Realism Journal. He was the final president of The ASCR and editor of the Classical Realism Newsletter. He wrote many articles and reviews in those publications. His essay “The Necessity of Excellence” was published in the book Realism in Revolution: The Art of the Boston School. He is the author of Richard F. Lack: An American Master and is co-author, with Kirk Richards, of For Glory and For Beauty: Practical Perspectives on Christianity and the Visual Arts. Gjertson is an ARC Living Master and an Aristos sponsor. He is listed in Who’s Who in American Art and Who’s Who in America.