Douglas Preston of the American Museum of Natural History wrote:
On March 31, 1905, during his junior year in College, Andrews was boating on the Rock River in bad conditions when his craft capsized; his friend, Monty White, died in the cold waters, but Andrews survived. After graduation the following year, Andrews used some of his money saved from taxidermy to travel to New York City to find a job at the American Museum of Natural History. Told that there were no openings, Andrews took a job as a janitor in the taxidermy department and began collecting specimens for the museum. During the next few years, he worked and studied simultaneously, earning a Master of Arts degree in mammalogy from Columbia University.
He married Yvette Borup in 1914. From 1916 to 1917, Andrews and his wife led the Asiatic Zoological Expedition of the museum through much of western and southern Yunnan, as well as other provinces of China. The book Camps and Trails in China records their experiences.
In 1920, Andrews began planning for expeditions to Mongolia and drove a fleet of Dodge cars westward from Peking. In 1922, the party discovered a fossil of Indricotherium (then named "Baluchitherium"), a gigantic hornless rhinoceros, which was sent back to the museum, arriving on December 19. In the 1920s, he went to Mongolia, hoping to find out something about the origin of man. He didn't find out anything about man, but he discovered a treasure trove of dinosaur bones. During four expeditions in the Gobi Desert between 1922 and 1925, he discovered Protoceratops, a nest of Protoceratops eggs, Pinacosaurus, Saurornithoides, Oviraptor and Velociraptor, none of which were known before.
On July 13, 1923, the party was the first in the world to discover dinosaur eggs. Initially thought to belong to the ceratopsian Protoceratops, they were determined in 1995 to actually belong to the theropod Oviraptor Walter W. Granger discovered a skull from the Cretaceous period. In 1925, the museum sent a letter back informing the party that the skull was that of a mammal, and therefore rare and valuable; more were uncovered. Expeditions in the area stopped during 1926 and 1927. In 1928, the expedition's finds were seized by Chinese authorities but were eventually returned. The 1929 expedition was cancelled. In 1930, he made one final trip and discovered some mastodon fossils. (Sixty years after Andrews' initial expedition, the American Museum of Natural History returned to Mongolia on the invitation of its government to continue exploration.) Later that year, Andrews returned to the United States and divorced his wife, with whom he had two sons.
In 1927, the Boy Scouts of America made Andrews an Honorary Scout, a new category of Scout created that same year. This distinction was given to "American citizens whose achievements in outdoor activity, exploration and worthwhile adventure are of such an exceptional character as to capture the imagination of boys...". The other eighteen who were awarded this distinction were: Robert Abram Bartlett; Frederick Russell Burnham; Richard E. Byrd; George Kruck Cherrie; James L. Clark; Merian C. Cooper; Lincoln Ellsworth; Louis Agassiz Fuertes; George Bird Grinnell; Charles A. Lindbergh; Donald Baxter MacMillan; Clifford H. Pope; George P. Putnam; Kermit Roosevelt; Carl Rungius; Stewart Edward White; Orville Wright.
Andrews joined The Explorers Club in New York in 1908, four years after its founding. He later served as its President from 1931 to 1934. In 1934, Andrews became the director of the museum. In his 1935 book The Business of Exploring, he wrote "I was born to be an explorer...There was never any decision to make. I couldn't do anything else and be happy." In 1942, Andrews retired to Carmel-by-the-Sea, California, where he wrote about his life and died in 1960. He is buried in Oakwood Cemetery in his hometown of Beloit.