In 1914 Reinhardt became a lecturer in English in the Extension Division of the University of California.
She was a member of the Town and Gown Club of Berkeley, Prytancan and English Club of the University of California, Phi Beta Kappa, the Dante Society of America, and Concordance Society of America.

After two years of teaching she was appointed president of the then-struggling Mills College in Oakland, California, at that time the only women's college on the West Coast and the second oldest women's college in the country.
Reinhardt succeeded acting president Hettie Belle Ege, who remained on the Mills faculty until 1930.
Arriving with her two young children, Reinhardt is said to have remarked that she was "the first college president who arrived on campus pushing a perambulator".
There she served from 1916 to 1943, through a period of substantial growth, making her the longest serving president in the institution's history.
During her tenure Mills constructed 17 additional buildings (growing from 11 to 28 total), increased enrollment three-fold in 15 years, and "gained national, even worldwide favor", including admission to the Association of American Colleges and Universities in 1917.

Reinhardt was active in local, national, and international organizations, lecturing and writing on topics including international cooperation, suffrage, and women's rights.
In 1919 she served the Oakland Chamber of Commerce as chair of the City Planning Committee, and she was regularly invited to speak at a range of organizations, such as the Retail Furniture Association of California, the Western Fruit Jobbers Association, the San Francisco Chamber of Commerce, and the Advertising Club of Los Angeles.

Starting in the First World War, Reinhardt worked as an advocate for world peace.
She supported Democratic President Woodrow Wilson's proposal to create the League of Nations, despite herself being active in the Republican Party.
In 1919 she traveled as a delegate to Tokyo for the meeting of the Institute of Pacific Relations, and in 1920 to Washington, D.C., to deliver a petition of 30,000 signatures from Californians urging the ratification of the Treaty of Versailles to end the war.
In total, she was a member of more than a dozen peace organizations over the course of her career.

In 1922 Reinhardt traveled again to Oxford and then to France as a representative of the American Association of University Women.
She served as vice president, and then in 1923, president of the Association, a position she held until 1927, helping to strengthen that organization significantly.
In 1928 she was a Republican elector from California, and opponent of Franklin D. Roosevelt's New Deal.
She continued her work with the Association of University Women into the 1930s, as chair of their Committee on International Relations from 1927 to 1933, also held the chair for the General Federation of Women's Clubs in their Department of Education from 1928 to 1930.
Then, during the 1936 presidential election, traveled as a delegate to the Republican National Convention.
In 1929 she again traveled to Japan in the interest of the Institute of Pacific Relations, this time meeting in Kyoto.

Reinhardt was a devoted and active Unitarian throughout her life.
In the 1940s she served as the first female moderator of the American Unitarian Association from 1940 to 1942, which according to contemporary news reports was the first time a large church in the nation had been represented by a woman.
Reinhardt served briefly as a minister at the First Unitarian Church of Oakland and delivered the Ware Lecture at the May 1932 meeting of the American Unitarian Association.
She also served for a decade on the board of directors at the Starr King School for the Ministry.
Reinhardt was the only woman member of the Unitarian Commission of Appraisal, commissioned to "study the church and find new directions for its re invigoration".

In 1945 Reinhardt was a delegate to the inaugural meeting of the United Nations in San Francisco, and spoke to numerous groups throughout the country, advoca
In 1914 Reinhardt became a lecturer in English in the Extension Division of the University of California. She was a member of the Town and Gown Club of Berkeley, Prytancan and English Club of the University of California, Phi Beta Kappa, the Dante Society of America, and Concordance Society of America.
After two years of teaching she was appointed president of the then-struggling Mills College in Oakland, California, at that time the only women's college on the West Coast and the second oldest women's college in the country. Reinhardt succeeded acting president Hettie Belle Ege, who remained on the Mills faculty until 1930. Arriving with her two young children, Reinhardt is said to have remarked that she was "the first college president who arrived on campus pushing a perambulator". There she served from 1916 to 1943, through a period of substantial growth, making her the longest serving president in the institution's history. During her tenure Mills constructed 17 additional buildings (growing from 11 to 28 total), increased enrollment three-fold in 15 years, and "gained national, even worldwide favor", including admission to the Association of American Colleges and Universities in 1917.
Reinhardt was active in local, national, and international organizations, lecturing and writing on topics including international cooperation, suffrage, and women's rights. In 1919 she served the Oakland Chamber of Commerce as chair of the City Planning Committee, and she was regularly invited to speak at a range of organizations, such as the Retail Furniture Association of California, the Western Fruit Jobbers Association, the San Francisco Chamber of Commerce, and the Advertising Club of Los Angeles.
Starting in the First World War, Reinhardt worked as an advocate for world peace. She supported Democratic President Woodrow Wilson's proposal to create the League of Nations, despite herself being active in the Republican Party. In 1919 she traveled as a delegate to Tokyo for the meeting of the Institute of Pacific Relations, and in 1920 to Washington, D.C., to deliver a petition of 30,000 signatures from Californians urging the ratification of the Treaty of Versailles to end the war. In total, she was a member of more than a dozen peace organizations over the course of her career.
In 1922 Reinhardt traveled again to Oxford and then to France as a representative of the American Association of University Women. She served as vice president, and then in 1923, president of the Association, a position she held until 1927, helping to strengthen that organization significantly. In 1928 she was a Republican elector from California, and opponent of Franklin D. Roosevelt's New Deal. She continued her work with the Association of University Women into the 1930s, as chair of their Committee on International Relations from 1927 to 1933, also held the chair for the General Federation of Women's Clubs in their Department of Education from 1928 to 1930. Then, during the 1936 presidential election, traveled as a delegate to the Republican National Convention. In 1929 she again traveled to Japan in the interest of the Institute of Pacific Relations, this time meeting in Kyoto.
Reinhardt was a devoted and active Unitarian throughout her life. In the 1940s she served as the first female moderator of the American Unitarian Association from 1940 to 1942, which according to contemporary news reports was the first time a large church in the nation had been represented by a woman. Reinhardt served briefly as a minister at the First Unitarian Church of Oakland and delivered the Ware Lecture at the May 1932 meeting of the American Unitarian Association. She also served for a decade on the board of directors at the Starr King School for the Ministry. Reinhardt was the only woman member of the Unitarian Commission of Appraisal, commissioned to "study the church and find new directions for its re invigoration".
In 1945 Reinhardt was a delegate to the inaugural meeting of the United Nations in San Francisco, and spoke to numerous groups throughout the country, advoca
Aurelia Henry Reinhardt