[2] During World War II, Campbell served in the United States Marine Corps.

After the war, he established a legal practice in Albuquerque, New Mexico, while working as an agent for the Federal Bureau of Investigation.

[2] In 1955, Campbell began his career in politics when he was elected to the New Mexico House of Representatives, where he served until 1962, after having spent the last two years as Speaker.

In 1962, he was the Democratic nominee for governor and defeated incumbent Edwin L. Mechem 130,933 to 116,184.

In office, Campbell supported programs to aid the mentally ill, and appointed the first state science adviser.