Fisher graduated from Lincoln High School in 1941 as valedictorian. She enrolled in the Arkansas Agricultural, Mechanical & Normal College (now University of Arkansas at Pine Bluff), but transferred to Langston University in 1942. After marrying in 1944, she graduated May 21, 1945, with honors.
Her brother planned to challenge segregationist policies of the University of Oklahoma, but went to Howard University Law School in Washington, D.C. to not delay his career further by protracted litigation.
Fisher was willing to delay her legal career in order to challenge segregation. In 1946, she applied at the University of Oklahoma and was denied because of race. Two years later, in 1948, the United States Supreme Court ruled in Sipuel v. Board of Regents of Univ. of Okla. that the state of Oklahoma must provide instruction for blacks equal to that of whites. Thurgood Marshall acted as the head NAACP lawyer for this case and the justices ruled unanimously. The case was also a precursor for Brown v. Board of Education.
In order to comply, the state of Oklahoma created the Langston University School of Law, located at the state capital. Further litigation was necessary to prove that this law school was inferior to the University of Oklahoma College of Law. Finally, on June 18, 1949, Sipuel was the first African-American admitted to the University of Oklahoma's law school. becoming the first African-American woman to attend a previously segregated, all-white public law school in Oklahoma. By this time, she was married and pregnant with the first of her two children. The law school gave her a chair marked "colored," and roped it off from the rest of the class. Her classmates and teachers welcomed her, shared their notes and studied with her, helping her to catch up on the materials she had missed.
Sipuel had to dine in a separate chained-off guarded area of the law school cafeteria. She recalled that years later some white students would crawl under the chain and eat with her when the guards were not around. Her lawsuit and tuition were supported by hundreds of small donations, and she believed she owed it to those donors to make it.
She graduated in 1951 with a Master of Laws degree and began practicing law in her hometown of Chickasha in 1952.
In 1992, Oklahoma governor David Walters appointed her to the Board of Regents of the University of Oklahoma, which she noted in an interview, "completes a forty-five year cycle." She further stated, "Having suffered severely from bigotry and racial discrimination as a student, I am sensitive to that kind of thing," and she planned to bring a new dimension to university policies.
Before her death in 1995, Fisher was a member of Alpha Kappa Alpha sorority and also was a professor at Langston University.
In 1996 she was inducted posthumously in the Oklahoma Women's Hall of Fame. The University of Oklahoma dedicated the Ada Lois Sipuel Fisher Garden in her honor.