Probably the greatest architect and designer Scotland has produced, he attempted to create a native style for the modern era. His decorative and graphic works are some of the finest manifestations of art nouveau while also being beautiful examples of early modernism. His few buildings are notable for their absence of external decoration and their subtlety of proportion—both qualities partially derived from Scottish medieval precedent and from the Scottish Baronial style of the 16th and 17th cent.

As a designer, Mackintosh was influenced in his early work by the English arts and crafts movement and, like the members of that school, he strove to integrate architectural and decorative elements in his work. Among his finest interiors were those executed for several turn-of-the-century Glasgow tea rooms. The sole survivor, the Willow Tea Room (1904), was restored and reopened in 1983. Many of his designs, often incorporating squares and stylized roses and other plant forms, were created in collaboration with his wife, Margaret Macdonald Mackintosh. Best known of his stark, elegant, and often beautifully detailed furniture designs are graceful wooden chairs with extremely high backs. He also designed other furniture, stained glass, murals, and clocks. His work influenced such important 20th-century figures as Josef Hoffmann and Frank Lloyd Wright.