World War I dominated campus life and the student body was “decimated” by enlistments for active service, with three hundred UBC students in Company “D” alone. By the war’s end 697 members of the university had enlisted. 109 students graduated in the three war-time congregations, all but one in the Faculty of Arts and Science.

By 1920, the university had only three faculties: Arts, Applied Science, and Agriculture (with Departments of Agronomy, Animal Husbandry, Dairying, Horticulture and Poultry). It only awarded the degrees of Bachelor of Arts (BA), Bachelor of Applied Science (BASc), and Bachelor of Science in Agriculture (BSA). There were 576 male students and 386 female students in the 1920–21 winter session, but only 64 academic staff, including 6 women.

In the early part of the 20th century, professional education expanded beyond the traditional fields of theology, law and medicine. Although UBC did not offer degrees in these fields, it began to offer degrees in new professional areas such as engineering, agriculture, nursing and school teaching. It also introduced graduate training based on the German-inspired American model of specialized course work and the completion of a research thesis, with students completing M.A. degrees in natural sciences, social sciences and humanities.

In 1922, the twelve-hundred-strong student body embarked on a “Build the University” campaign. Students marched through the streets of Vancouver to draw attention to their plight, enlist popular support, and embarrass the government. Fifty-six thousand signatures were presented at legislature in support of the campaign, which was ultimately successful. On September 22, 1925, lectures began at the new Point Grey campus. Except for the library, Science and Power House buildings, all the campus buildings were temporary constructions. Students built two playing fields, but the university had no dormitories and no social centre. Still, the university continued to grow steadily.

Soon, however, the effects of the depression began to be felt. The provincial government, upon which the university depended heavily, cut the annual grant severely. In 1932–33, salaries were cut by up to 23%. Posts remained vacant, and a few faculty lost their jobs. Most graduate courses were dropped. In 1935, the university established the Department of Extension. Just as things began to improve, World War II began and Canada declared war on September 10, 1939. Soon afterwards, University President Klinck wrote:

From the day of the declaration of war, the University has been prepared to put at the disposal of the Government all possible assistance by way of laboratories, equipment and trained personnel, insofar as such action is consistent with the maintenance of reasonably efficient instructional standards. To do less would be unthinkable.

Heavy rains and melting snowfall eroded a deep ravine across the north end of the campus, in the Grand Campus Washout of 1935. The campus did not have storm drains, and surface runoff went down a ravine to the beach. When the university carved a ditch to drain flooding on University Avenue, the rush of water steepened the ravine and eroded it back as fast as 10 feet (3.0 m) per hour. The resulting gully eventually consumed 100,000 cubic yards (76,455 m3), two bridges, and buildings near Graham House. The university was closed for 4 and a half days. Afterwards, the gully was filled with debris from a nearby landslide, and only traces are visible today.

Military training on the campus became popular, then mandatory. WWII marked the first provision of money from the federal government to the university for research purposes. This laid a foundation for future research grants from the federal government of Canada.