Born in Honolulu, Hawaii, Ariyoshi graduated in 1944 from McKinley High School. As World War II drew to a close, he served as an interpreter with the U.S. Army Military Intelligence Service in Japan. Upon returning stateside, he first attended the University of Hawaii at Manoa, then transferred to Michigan State University, where he graduated with a Bachelor of Arts degree in 1949. He then went on to receive his law degree from the University of Michigan Law School.
Ariyoshi's political career began in 1954 when he was elected to the Hawaii Territorial House of Representatives as a Democrat. He was later elected to the Territorial Senate in 1958, then to the State Senate in 1959. He served in the Senate until 1970, when he ran for and was elected Lieutenant Governor in 1970 with Governor John A. Burns.
When Gov. Burns fell ill in October 1973, Ariyoshi became Acting Governor. In the election of 1974, he was elected Governor of Hawaii in his own right, with Nelson Doi as his first Lieutenant Governor. He was re-elected in 1978 (with Lt. Gov. Jean King) and in 1982 (with Lt. Gov. John Waihee).
Ariyoshi's administration was marked by fiscal conservatism, as the post-statehood economic boom came to an end. He guided the state through its first economic recession.
Barred by term limits from seeking another term in 1986, Ariyoshi was succeeded by Lt. Gov. Waihee. After leaving public office, he served in a variety of corporate and non-profit capacities.