After graduating from Harvard, Brook officially started his photographic career, opening a portrait studio on Newbury Street in 1946.

This was a significant step for photography in Boston, a medium that was steadily increasing its presence in museum and gallery exhibitions and collections. Brook began showing his work in Boston’s Sidney Kanegis Gallery in 1955, and exhibited in galleries and museums across the United States and Europe in the first decades of his career.

In 1966 Brook was one of several photographers, including Jules Aarons, Harry Callahan, Paul Caponigro, and Minor White, who exhibited work in a group show at the reopening of the Carl Siembab Gallery on Newbury Street, where Brook showed frequently. In 1961 Brook's photography was the subject of the inaugural exhibition in a newly designed gallery at the George Eastman House. He was one of twenty photographers shown at the Kodak Pavilion of the 1970 World’s Fair in Osaka, Japan.

Brook’s photography appeared in Aperture, Art in America, Art News, Aura, Camera, Contemporary Photographer, Life, Modern Photography, Newsweek,  Vita Fotografica,  among others. His numerous awards included the gold medal at the 3rd International Biennial in Milan. Brook published two books, A Long the Riverrun (1970) and Hold Me (1977), featuring his timeless, romantic, pictorialist views.

Brook was an active member of the Boston art world in the decades when the school of Boston Figurative Expressionism was thriving. While the focus of the movement, which emerged from the School of the Museum of Fine Arts in the late 1940s, has historically been painting-centric, other media, including photography, had a significant presence. Brook captured the era in photographs of friends and their families in a style that was distinctively his — soft-focused, enhanced attention to light and shadow, an emotional connection to the subject, overt symbolism, a profound consideration of human relationships — and how all visually translated to a work of art.

His attentiveness to the technical innovations of the photographic process is apparent across multiple series and subjects, in both personal works and commissions. A chance optical aberration in a portrait of a father and child led to his experimentation with lenses, which he would often build himself. Commissioned portraits have a distinctive soft-focused flare to them, with settings reminiscent of an earlier time.

Brook seemed to relish the idea of being of another time. In an anecdote regarding an exhibition at the Carl Siembab Gallery in 1970, Brook recalled that Siembab described him as a photographer who took “100 year-old pictures every day.” He often described his work in otherworldly terms, as illustrations of thoughts and fantasies, and not necessarily grounded in reality. He wrote of seeking beauty in his works in a way that placed his philosophy in the realm of the social and cultural mores of the late-nineteenth-century Aesthetic Movement, whose artists asserted the authority of beauty as the force behind all aspects of daily life.

Brook’s works, in both subject matter and style, are also closely aligned with the Pictorialist movement of the turn of the twentieth century. Pictorialists sought to establish photography as a fine art through carefully chosen and idealized subject matter, soft focus, and low tonal gradation. A pictorial landscape was a romantic pastoral escape, and figures symbolized ideals of beauty. Brook’s veneration of the human form closely aligns him with pictorial photography, and he is perhaps most known for his soft-focused representations of the nude.

Works appearing in A Long the Riverrun and Hold Me included male and female figures, both alone and together, posed in sun-dappled natural settings. Brook unabashedly sought the beautiful in his work, describing a process where he “found beautiful people, places, and moments in a world that was getting uglier every day.”