Muir began publishing articles and essays on nature and conservation in various magazines, including Overland Monthly and Century Magazine. These writings helped to build his reputation as a naturalist and conservationist.

Muir's writings and advocacy played a crucial role in the establishment of Yosemite National Park in 1890. His articles helped to raise public awareness of the park's natural beauty and the need for its preservation.

Muir co-founded the Sierra Club, a leading environmental organization dedicated to protecting and exploring wild places. He served as its first president, a position he held until his death.

Muir published several influential books, including 'The Mountains of California,' 'Our National Parks,' 'My First Summer in the Sierra,' and 'Stickeen.' These books further popularized his ideas about nature and conservation.

Muir camped with President Theodore Roosevelt in Yosemite, influencing the president's conservation policies. Roosevelt later designated several national parks and monuments, inspired in part by Muir's advocacy.

Muir fiercely opposed the construction of a dam in the Hetch Hetchy Valley, a Yosemite-like valley in Yosemite National Park. Although he lost the battle, the controversy raised public awareness of conservation issues and helped to galvanize the environmental movement.