Born in Carey, Idaho, Pete attended the University of Idaho, where he was a member of the Vandals' boxing team and the Tau Kappa Epsilon fraternity. He graduated with a bachelor's degree in agriculture in 1940 and taught math and science and coached in Carey, Cambridge, and Glenns Ferry. During World War II, he was an aviator in the Marine Corps.
Cenarrusa was elected to the Idaho House of Representatives from Blaine County in 1950. He served in that capacity for 16 years, including six as speaker of the house.
In 1967, Cenarrusa was appointed Secretary of State by Governor Don Samuelson to fill a vacancy caused by the death of Edson H. Deal,and took office on May 1. Pete was elected to a full term in 1970. He was reelected seven times (1974, 1978, 1982, 1986, 1990, 1994, and 1998). Upon leaving office Pete was the longest-serving secretary of state in the United States. He's also the longest-serving elected public official in Idaho history, having held elective office for a total of 52 years.